As Raze said, your trainer can help you with that. You can buy an increase in maximum skill levels at your trainer. The first step is from 5 up to 10, after that comes up 10 up to 13. This makes especially Mage characters almost invincible. Combine a lvl. 13 Magic Missile with Mana Effecieny (magic is cheaper, passive) and Destruction (magic does more damage, passive) and you're really going to be a hard challenge for your enemies.
