Upgrading ram - how?

C86G

(excuse me for creating two threads in this sub in one day)

I´d like to upgrade my Ram but I am not sure how to proceed. Should I get two similar (or the same) modules or buy two larger ones? I´ve done a bit of reading but I am still not sure what´s best. My mainboard has 4 Ram slots, two are used by a 4GB module each.
Oh, and I am running Win7 64.

throttlekitty

You download it, of course!  

You'll want to match the speed and size of what you have in there. Personally I'd try for getting the same model in if possible simply for the sake "safety" (read: I don't really know what happens when the finer points don't match, like CAS Latency). But at least get the same frequency, the system will use the slowest across the board if you had say a PC3200 and PC2400. Same size is important for dual-channel operation.

Prime8

As said, try to get the same modules to be on the safe side, though PCs today are not so picky about mixing different models.
Don't know the current prices but might be worth checking the for 8GB modules as well.

Daf57

Your board will take 32GB - you can max it out for less than $200. Crucial will ship matching modules.
http://www.crucial.com/usa/en/b75-pro3-m/CT2910107