I'm trying to change the rims on the default van. I noticed due to the creation of the wheels, there are hidden spots not filled. I looked at the day care van and that is all one big circle. I'm using an image online that I would use, but wanted to use a green circle to get the point across better.

How difficult is it get so the default can be similar to the day care one? What programs would I need to use? I presume it has something to do with the joints or bones, but unsure exactly how to modify those.