You mean swap your car for the Mercedes on the current loan? No you can not.
You can trade it in and get a new loan for the Mercedes. But you will pay far more than $13,500 because the dealer won't give you anywhere near $12k for your Suzuki. More like $7000. Which leaves you with $5k negative equity which will be added to the Mercedes. Making it $18,500 + tax, title, license.