Adding memory...

I'm familiar with macs, but just bought a 2009 imac and would like to add more memory. I know how to physically do it, I just don't know HOW much I can add? Can I add as much as I want? It has 2 GB now but I'd love to get it as high as possible? Please advise

I'd suggest going to Crucial and using the system scanner. It will tell you what you have already and give you all the possible upgrade options.