Try this
cmd.CommandText = "UPDATE Customers SET [First Name]='" + Customer.GetFirstName() +
"', [Last Name]='" + Customer.GetLastName() +
"', [Address]='" + Customer.GetAddress() +
"', [Phone Number]='" + Customer.GetPhoneNum() +
"', [Email Address]='" + Customer.GetEmailAddress() +
"' WHERE [Customer ID]=" + editIdTB.Text;