Switching main gmail account

I have a few gmail accounts. When I got the Eris the sales guy had me enter my gmail info to set up the phone. Well I wasn't at all familiar with exactly what this would do. The account I entered gets a ton of junk mail and has contacts that I don't need. I want to set it up with my other account that doesn't get all of the junk mail and whatnot. It is basically a clean account. Is it possible to switch the main gmail account on the phone???

I hope that someone else has another solution, but the only way I would no how to do it would be to do a "hard reset."

Menu-Settings-Security-Factory Data Reset.

That would make the phone like it just came out of the box.