It is simple but potentially messy, if you drop the old one in the bilge!
I like to:
1) turn off the battery switch if you have one
2) I like to take a c-clamp and clamp off the fuel line just to prevent leaks although the anti siphon valve should really suffice here.
3) I put a big coffee can under the area where the filter is if there are any spills
4) use an oil filter wrench to spin off the filter, make sure you are turning it the right way
5) carefully remove the full of gas filter and dump it into a big glass jar. Then let it settle, look for a layer of water on the bottom
6) lube the filter gasket with motor oil, I like to put some on the mounting boss on the filter base too
7) fill the filter 3/4 full with clean gas
install filter hand tight, 3/4 turn after the gasket touches the mounting boss....