Barbara I use a scraper blade to do it.
Page 179-I have used both.
They are both designed to do exactly this job and it clearly states this in the catalog.
Now I know just how we tend to be here and I can understand why mostly but this is a specific case where I have tried other brand cheapo copies of these blades designed just for FGRV patrons and they are not the same. If you damage your finish because of this and because you are too cheap to buy the real deal remember I cautioned you here first.
You will notice that the blade needs to be angled just right to remove the old crap effortlessly and will gouge the gelcoat otherwise so as Jim suggests try it somewhere hidden first if you can.
When removing the stuff almost no pressure is needed as soon as you get the blade angle right it will just peel it off almost by itself.
After the stuff you can see has been removed (in about 5 minutes max) then I would use a solvent to get the residue and remainder of it off of the gelcoat.