how do i reset my network credentials

When you access a shared folder on some other machine (e.g. when backing up your files to that machine) then you must supply an account and a password that is acceptable to that machine. In other words, an account/password must exist on the other machine that you are aware of. The message you now see can mean any of the following:
a) The other machine is no longer visible from your machine.
b) It has a different name than it used to have.
c) The previously shared folder no longer exists.
d) You have lost your access rights to that folder.
e) The account you used no longer exists on the other machine.
f)The password on the other machine has changed or expired.

You now need to check each of these six conditions until you find which one causes you a problem.

Note also for your next post in this Community Group that you need to post full details of your problem if you require a good reply. Your initial question (my credentail password or user name has expired. that is the message i get on the bottom of my computer. how do i reset them?) would have prompted nothing other than a few wild guesses.