Switch SL 500 to SLK 55, SLK350?

I have an SL 500 (2002). I could now (without taking a lot of coal in my hand) switch the SL 500 into a SLK 55 according to the offer of my MB branch office? What does this mean? Both are absolutely great bolids. I even study to switch the SL 500 into an absolutely top equipped SLK 350 (Designo, …), especially since both have similar driving performance.