Start by getting valuations on your car, then you need the settlement figure on your car to see if you have equity, that will depend on how much deposit you paid, if it was minimal then there is a good chance you'll be in negative. Trying to get a discount on used can be a challenge but you may find a deal is out there if the dealer has a good margin in the car, you won't know until you ask. The apr is taking the micky, a bank loan would be cheaper or try a third party such as Oracle, or if you have a Halifax account they offer a car buying scheme, the dealer may reduce the rate if they think they have competition.