I want to change the wheels of my Audi A6. But got some questions not sure about them. Is there anybody has experience on changing the wheels?

Current the wheels on my car is : konig crosshairs, 18*8.5, the tires are 225/40/R18. I just found a set of wheels which are 18"*8 and another set of wheels with tires are: 18*8.5 and 255/45/R18.
The question is can I just buy the set of 18*8 wheels and install my current tires? Since my tires are pretty new just bought them several months.

Or should I buy another set of wheels with tires, the problem of them are the tires have only 25% left. I wonder my tires of 225/40/R18 can fit on that wheels?

Anybody have any congestion on my problems?

Thanks a lot