Usually heat will work. A heat gun works but be careful not to overheat. A hair dryer may work too and is less likely to scorth the finish. There may very well be a ghost image of the old name when the decals are removed since the gel coat may have faded a bit where the decals weren't. If so, it can be difficult to get rid of the images.
All that aside, if you are superstitious, there are procedures to remove a name and rename a boat. I won't go into all the details but at a minimum it is bad luck for the new owner to remove the old name. You need to have somebody else do the job.
Of course if you are OK tempting fate, go ahead