Finally i got my answer:
protected void btnSubmit_Click1(object sender, EventArgs e)
{
string DepartmentID = ddlDepartment.SelectedValue;
string Description = tbImageName.Text.Trim();
string Priority = ddlPriority.SelectedValue;
string imgName = fileuploadimages.FileName.ToString();
string imgPath = "Images/Departments/" + "" + ddlDepartment.SelectedValue + "/";
bool IsExists = System.IO.Directory.Exists(Server.MapPath(imgPath));
if (!IsExists)
System.IO.Directory.CreateDirectory(Server.MapPath(imgPath));
fileuploadimages.SaveAs(Server.MapPath(imgPath + imgName));
con.Open();
SqlCommand cmd = new SqlCommand("Update Images set Priority=Priority+1 where Priority>='" + ddlPriority.SelectedValue + "'" + "Insert into Images(ImageName,Description,Path,Priority,DepartmentID) values(@ImageName,@Description,@Path,@Priority,@DepartmentID)", con);
cmd.Parameters.AddWithValue("@ImageName", imgName);
cmd.Parameters.AddWithValue("@Description", Description);
cmd.Parameters.AddWithValue("@Path", imgPath + imgName);
cmd.Parameters.AddWithValue("@Priority", Priority);
cmd.Parameters.AddWithValue("@DepartmentID", DepartmentID);
cmd.ExecuteNonQuery();
con.Close();
tbImageName.Text = string.Empty;
}