Vehicle refinancing

Hello together, maybe someone can give me some information so that I don’t run directly into the “open” knife. My car dealer approached me because of another car… First of all, I bought a car 11/2008, but financed… The total amount of money is a little over 8000 euros. So 13 months I pay now to about 136 €. Now I think about because bigger inspections and works are pending, if I don’t refinance the car… Specifically it’s the Golf 4, the i Now I have to exchange golf 6 for an annual car.. Somehow this seems too expensive for me… According to DAT, the car has a value of 4800 €. But the new one is supposed to cost 17800 €. If I now count 13x 136 € I come to a little more than 1700 €. But with that I still have to finance 7000 €… So if this is to work, then the VW dealer would have to give me the 7000 that are still open so that I could finance the new one at all… I can’t just almost 18000 pay. I wonder, because it seems a bit utopian to me… Is that even possible? I don’t want to pay two cars at the end or overfinance it. Then I leave it… Does someone have experience and could give me valuable tips? Thank you… Best regards, Jimmy