It may not be possible to fix it. The Xbox 360's hardware is extremely outdated at this point, and BF3 was designed more for current PCs than consoles. Granted, the game should probably look at least as good as BC2 on console. I think the console version simply got a somewhat subpar port as far as graphics go. DICE probably elected to put more effort into the PC version because the consoles simply aren't capable of running the game they wanted to make, not without making huge sacrifices.