If you mean changing an existing user password, then you can do that with the UPDATE statement.
It would be appreciated if you can show some effort on work done so far and then also give info on any error/challenge encountered.
Friend you are not giving us enough clues to help you.
We'll need a better understanding of what you mean password change while the form is executing. Also we'll need to see some code in order to give you a solution that matches your code (apart from showing effort). ie Do you keep your password stored in a db or is it in an encrypted text file because your program has nothing to do with dbs?
Set the TextBoxPassword.Text to String.empty while the form is executing. That will set it to String.Empty while the form is executing. You could also set the TextBoxPassword.Text to "What the hell are you talking about" while the form is executing.