Honestly, you probably need not mess with that for a few thousand rounds.
I do not know how to disassemble the FNP slide, but there is a "how to" here on the site.
I can disassemble my Walther P99 slide very easily, however. And, as I use CCI Blazer ammo (which is pretty clean), when I took my slide apart at 2k rounds, I found that it was hardly dirty at all. Wasn't even worth dealing with.