Ok, i know this is a stupid question but who do you have to talk to in order to become a mage?

Not stupid at all... You need to find Mebbeth, the midwife in the Ragpicker's Square. You'll have to do some quests for her and she'll teach your the Arts.

Well if you haven't left gotten to any of the Wards yet then you can use Mebbeth, like Tal says, she's in the Ragpicker's Square and requires you to do some quests first. After Mebbeth has taught you you can use Dak'kon at any time to change you back.
If you're in the wards alredy then use Sebastian, he is in the Lower Ward near the foundry, you might have to kill Grosuk for him first before you get the option, I'm not too sure on that one.
After that there's the old lady in Curst (Not Gone) in the Tavern.
I think that's about it...

Thanks, i needed that.