I've been looking to replace my Xfire with a BMW 535i Y-reg (2001). I found the one I wanted at about £17.5k

My Xfire has just over £22k left on the finance. I just want them to take it off my hands and clear the finance for me, but... the trade price for the Xfire is only £17k!!!!!!!!!! Jeez, I'm £5k negative equity to get rid of the car. What can I do?!