How do u beat the elite 4 in pokemon white?

Beating the E4 with one super Pokemon is pretty hard in comparison to having six well-trained Pokemon. In Pokemon Black and White, however, you shouldn't have too much of a problem considering types... I would recommend grinding a few levels, buy potions and revives, primarily use Surf and Slash, only use Hydro Pump when you absolutely need it. Take it from a veteran trainer.