Levels aren't as important in Final Fantasy Tactics as abilities are. You can be twice the level of the people you are fighting (as you probably will be in this case) and still lose utterly.

If you want to go about it the easy way, make sure Ramza has Yell, and Accumulate wouldn't hurt either. Simply run away from Wiegraf and keep Yelling until your speed is really high, then Accumulate until your attack is really high. After that, you should have no trouble defeating that fight. The next fight, however, you may wish to have some Ninja in order to keep Rafa alive.