Super Smash Bros Brawl Lag fix?

[nwycoff37]

When playing super smash bros brawl with 4 characters the frame rate goes from 100% to 57% and the audio and start to lag. Its nothing to do with my cpu or ram cause they dont sky rocket at all when playing. Im pretty sure its my GPU and graphics card. are there any solutions? like drivers that i can download or anyway to downgrade the graphics a little bit?