If you own "The Sims 2 University" and "The Sims 2 Seasons" installed, you can change the seasons at the colleges. At the top left part of the screen in the college neighborhood view there is a seasons button. Click on that button to customize the order and which seasons appear. They can be anything you want!
While you can pick any seasons you want, I suggest making the majority, if not all, the seasons fall. During the fall season, Sims are able to build skills faster. Homework and skill building is incredible fast, leaving your Sims more time for socializing or just building more skills.