Why code first migration no update table that exist in database?

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ASP.NET

C#5.0

entity-framework

I want Update database by code first migration .for example I have 3 entity in contex and 1 table in database and there is a problem when I run program and get this error:There is already table.


Migration Configuration

 internal sealed class Configuration : DbMigrationsConfiguration<ApplicationDbContext>
{
    public Configuration()
    {
        AutomaticMigrationsEnabled = false;
       // AutomaticMigrationDataLossAllowed = false;
    }

    protected override void Seed(ApplicationDbContext context)
    {
        //  This method will be called after migrating to the latest version.


    }
}

IdentityModel

public ApplicationDbContext() : base("DefaultConnection" )
    {
        Database.SetInitializer<applicationdbcontext>(new MigrateDatabaseToLatestVersion<applicationdbcontext,>());
    }

What I have tried:

I have try update database that is already but I can do it.</applicationdbcontext>