I have an older road bike and I am looking to renovate it. The frames
on my wheels are pretty thin, and I very much like the look of thicker
frame wheels, can I produce this effects without buying new wheels
completely, seeing as they are kind of expensive?
Short answer: No. There is no product out there to make a rim look wider. Just wider rims. Which may or may not fit your bike.
However, if you tell us what size tires you have, provide the make & model of the bike & maybe some pictures of the frame where the tires run closest, we may be able to advise you as to whether or not you can fit wider tires. Also, I am assuming that when you say “frames on my wheels” you mean the rim.
Don’t paint the wheels. First of all if you have rim brakes (most likely) the paint will damage the bikes ability to slow effectively while braking & would eventually be rubbed off by the brakes anyway. Also, after a few miles with maybe a little gravel or road debris, the paint will chip & look trashy.
As for painting the frame, if you can afford to, you should really consider having it professionally powder coated. Even a well done spray can job will scratch easily & not last anywhere near as long as a powder coat job.
If you insist on painting it yourself, either sand blast the original finish off & then clean with an evaporating residue free solvent, or at the very least remove any and all decals or stickers, clean with solvent, roughly sand the entire surface, clean with solvent again & then paint.