I want a new car but i have a finance car?

i own a 2006 Lexus is250, and recently test drove a Honda Civic Si. I personally am looking for a manual car. So therefore i got bored of the lexus.

Now the problem is that i still owe money on the lexus. The honda i test drove is less then what i owe on the lexus. What happens to the balance on the lexus. Do they add it to the new balance or do they offer to pay the rest off? Would this also hurt my credit score?

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