I found this lovely website for cleaning and oiling my wonderful overlocker - pictures & all!
Cleaning the bottom of the machine
Photo from website mentioned
I had never removed the bottom of my overlocker to clean that out, and you could tell as much when I did!! Oh brother, I uncovered an army of fabric-dust mice under there.
Whatever brand of machine you have, chances are there will be a guide online on how to clean and oil it, you may even be lucky & find a YouTube video for your specific machine, but here is a good one for general machine cleaning.
There are many parts to this - be sure to watch them all.
Go on, get cleaning!!!