I found an easier way that works for me. Type in the first letter of your user name, auto-complete will bring up a box of choices. Highlight the username you want to use. Hit the "delete" key. Another auto complete window will pop up saying, "windows has
a stored password for this user name. Do you want to delete the username and password?" Click, "yes". Close explorer window and when you reopen you should be able to type in your user name and password and it should ask , "do you want to save this password?"
I'm no expert, but this worked for me. And I have done it more than once. Hope this helped.