3M and a few other companies make rubber wheels that go on a power drill or grinder that are specifically made for removing applied decals without damaging paint. You can get one at any store that sells auto finishing supplies. The good ones create enough friction to warm the decal loosening it and then strip it away in small bits. It can be a bit tedious working on the tubes of a bike as it was designed for use on cars and trucks with larger, flatter surfaces. Goof Off will work for those areas that can't be reached with the disc and for a final wipedown to remove residue.

If you remove decals on an older bike, the paint underneath may no longer match due to fading and etching of the surrounding paint. Sometimes you can fix this with rubbing compound followed by a polishing compound. Sometimes that isn't enough and you have to either live with it or redo the paint job.