Be very, very, careful.
There are differences between sanding and compounding and polishing. Different equipment, different speeds, different "gunk". And once you damage whatever gelcoat is left--it is gone and you are left with a cycle of painting and repainting the hull.
I would try the most gentle approach (polishing) first to see how that & waxing gets you through the next season. 3M makes a full line of products for this, and any auto body/refinishing supply store can sell them to you. 3M also has great toll-free support for all of their products.
It is very easy to get impatient or aggressive and do permanent damage, so take your time. See if you can get a video from online "how to" video places, or a book from the local library.