Your user ID is the number on the back of your Polar Express card (see image below).
If you don't know your library PIN number, contact the Circulation Desk, (907) 474-6762.
Note: If you're needing to renew items that you borrow via Interlibrary Loan (ILL), login to your ILL account [3].
Links:
[1] http://uaflibrary.us/media/equipment/#renew
[2] http://goldmine.uaf.edu/uafandbiosci
[3] http://uaf.illiad.oclc.org/illiad/logon.html