I had this experience, except that it was 10 years! What I did was to send them a letter reminding them of the courses I took and then sending them papers I had written in those courses along with my transcripts. Now I work at a college and write recommendation letters and I know that actually these are very difficult to do because you don't remember specific details. To get the best possible recommendation, give the person as many concrete examples as you can of things they can write about you. You might want to give them a transcript, and tell them about your experiences since college. I've written a hub about getting a good recommendation, if you want more ideas.