How to decrypt password

public static string ComputeHash(string plainText, string hashAlgorithm, byte[] saltBytes)
        {
            // If salt is not specified, generate it.
            if (saltBytes == null)
            {
                // Define min and max salt sizes.
                int minSaltSize = 4;
                int maxSaltSize = 8;

                // Generate a random number for the size of the salt.
                Random random = new Random();
                int saltSize = random.Next(minSaltSize, maxSaltSize);

                // Allocate a byte array, which will hold the salt.
                saltBytes = new byte[saltSize];

                // Initialize a random number generator.
                RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider();

                // Fill the salt with cryptographically strong byte values.
                rng.GetNonZeroBytes(saltBytes);
            }

            // Convert plain text into a byte array.
            byte[] plainTextBytes = Encoding.UTF8.GetBytes(plainText);

            // Allocate array, which will hold plain text and salt.
            byte[] plainTextWithSaltBytes =
            new byte[plainTextBytes.Length + saltBytes.Length];

            // Copy plain text bytes into resulting array.
            for (int i = 0; i < plainTextBytes.Length; i++)
                plainTextWithSaltBytes[i] = plainTextBytes[i];

            // Append salt bytes to the resulting array.
            for (int i = 0; i < saltBytes.Length; i++)
                plainTextWithSaltBytes[plainTextBytes.Length + i] = saltBytes[i];

            HashAlgorithm hash;

            // Make sure hashing algorithm name is specified.
            if (hashAlgorithm == null)
                hashAlgorithm = "";

            // Initialize appropriate hashing algorithm class.
            switch (hashAlgorithm.ToUpper())
            {

                case "SHA384":
                    hash = new SHA384Managed();
                    break;

                case "SHA512":
                    hash = new SHA512Managed();
                    break;

                default:
                    hash = new MD5CryptoServiceProvider();
                    break;
            }

            // Compute hash value of our plain text with appended salt.
            byte[] hashBytes = hash.ComputeHash(plainTextWithSaltBytes);

            // Create array which will hold hash and original salt bytes.
            byte[] hashWithSaltBytes = new byte[hashBytes.Length +
            saltBytes.Length];

            // Copy hash bytes into resulting array.
            for (int i = 0; i < hashBytes.Length; i++)
                hashWithSaltBytes[i] = hashBytes[i];

            // Append salt bytes to the result.
            for (int i = 0; i < saltBytes.Length; i++)
                hashWithSaltBytes[hashBytes.Length + i] = saltBytes[i];

            // Convert result into a base64-encoded string.
            string hashValue = Convert.ToBase64String(hashWithSaltBytes);

            // Return the result.
            return hashValue;
        }

public static string ComputeHash(string plainText, string hashAlgorithm, byte[] saltBytes)
{
    // If salt is not specified, generate it.
    if (saltBytes == null)
    {
        // Define min and max salt sizes.
        int minSaltSize = 4;
        int maxSaltSize = 8;

        // Generate a random number for the size of the salt.
        Random random = new Random();
        int saltSize = random.Next(minSaltSize, maxSaltSize);

        // Allocate a byte array, which will hold the salt.
        saltBytes = new byte[saltSize];

        // Initialize a random number generator.
        RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider();

        // Fill the salt with cryptographically strong byte values.
        rng.GetNonZeroBytes(saltBytes);
    }

    // Convert plain text into a byte array.
    byte[] plainTextBytes = Encoding.UTF8.GetBytes(plainText);

    // Allocate array, which will hold plain text and salt.
    byte[] plainTextWithSaltBytes =
    new byte[plainTextBytes.Length + saltBytes.Length];

    // Copy plain text bytes into resulting array.
    for (int i = 0; i < plainTextBytes.Length; i++)
        plainTextWithSaltBytes[i] = plainTextBytes[i];

    // Append salt bytes to the resulting array.
    for (int i = 0; i < saltBytes.Length; i++)
        plainTextWithSaltBytes[plainTextBytes.Length + i] = saltBytes[i];

    HashAlgorithm hash;

    // Make sure hashing algorithm name is specified.
    if (hashAlgorithm == null)
        hashAlgorithm = "";

    // Initialize appropriate hashing algorithm class.
    switch (hashAlgorithm.ToUpper())
    {

        case "SHA384":
            hash = new SHA384Managed();
            break;

        case "SHA512":
            hash = new SHA512Managed();
            break;

        default:
            hash = new MD5CryptoServiceProvider();
            break;
    }

    // Compute hash value of our plain text with appended salt.
    byte[] hashBytes = hash.ComputeHash(plainTextWithSaltBytes);

    // Create array which will hold hash and original salt bytes.
    byte[] hashWithSaltBytes = new byte[hashBytes.Length +
    saltBytes.Length];

    // Copy hash bytes into resulting array.
    for (int i = 0; i < hashBytes.Length; i++)
        hashWithSaltBytes[i] = hashBytes[i];

    // Append salt bytes to the result.
    for (int i = 0; i < saltBytes.Length; i++)
        hashWithSaltBytes[hashBytes.Length + i] = saltBytes[i];

    // Convert result into a base64-encoded string.
    string hashValue = Convert.ToBase64String(hashWithSaltBytes);

    // Return the result.
    return hashValue;
}