All it will do is change the look and cost you more money to buy (4) 20” wheels and then have to buy 4 tires to fit. In addition, if you price the exact same tire (brand / model) in a 17” VS 20” (equivalent height and width) it will almost always cost more money for the 20” tire...Sometimes substantially more money even though they are the same overall height and width. If you are trying to do so because of appearance, you’re not limited to those 2 sizes. You can put an 18” for example. What are you trying to accomplish?