Hello there, I just read at another post a guy who changed his GPU 6970 1GB for a 2GB one, I got the base model with 512MB (bad move getting this one) and I really don't want to change the whole computer, can I upgrade to the 6970 1GB? (or even the same 6770 but with 1GB VRAM? If so, where can I do this? apple? any other site?