It would help to know the version of OST that you are using. Assuming that you are on 1.6.rc2:
to upgrade read the following thread:
http://www.osticket.com/forums/showthread.php?t=255(http://www.osticket.com/forums/showthread.php?t=255)
and the upgrade guide:
http://osticket.com/wiki/Upgrade_and_Migration#osTicket_v1.6_RC2_to_v1.6_RC3(http://osticket.com/wiki/Upgrade_and_Migration#osTicket_v1.6_RC2_to_v1.6_RC3)
my only recommendation is that when reading the upgrade guide, where it says "Once you've overwritten the files, rename config.php to ostconfig.php"...just pass by that step and don't do it. My initial upgrade attempt did this, and all I got was a white page. I renamed it back to config.php and all is fine.
later...
jason...