So I'm trying to upgrade the memory in my iMac that I bought in early 2011, before the last refresh. It seems like there are 4 memory slots, but the standard build unit you get from Apple only comes with 2 slots full (2x2gb). What would be the best way to upgrade my memory? I'm thinking I want to double it at least, but I'm not to sure how to proceed since this would be my first time upgrading anything with the Mac lineup. I hear it's pretty simple to actually upgrade the memory. But picking which brand is best, and which configuration is a little daunting so any help would be appreciated. Thanks!