By reducing your monthly outgoings, can I assume that you have bought it on a finance deal of some sort? If that is the case, then you haven't actually paid out £25,000 for it. You have paid out your deposit, plus however many monthly payments you have made. Assuming that you have some equity in it, if you sell it and pay off the finance, it will have cost you your deposit, plus monthlys, less the equity that you get back. So maybe less than £6,000.
If you put in a small deposit when you bought it, the chances are is that you are in negative equity, so will have nothing in it to start again with on a new deal. I'm sure that dealers will be able to manipulate the figures to do a deal to put you in another car with lower monthly payments, but that would mean rolling the debt over into the next car, which in turn makes that car ultimately more expensive.
The debt needs to be paid off at some point, so you would be better off in the long run by sticking with it, cut back on other stuff and get the car paid for. Do that and you will be on a much stronger footing next time.