Hmm, just attack his monsters? Use your abilities better? Check if you used all the skillbooks, they're in the part of inventory with an apple (if I recall?) on it, and if not then use them and put them into some battle skills you already developed a lot.
If you can't develop some skills past level 5, go to your instructor in the tower and buy the allowance to upgrade them more, just before Bellegar catches you.
