Development of a Wizard hero from the Haven faction.

While playing the first mission of the campaign for the Haven faction, I encountered a problem: the main hero (Anton) has no third-level spells. In other words, magic can only be developed up to the second level. As I understand it, this is because the hero has a preference for strength rather than magic. Is there a way to change this, or is he destined to be a warrior and not a mage?