Depends on the pump. If yours has a metal cap that's held on with a single screw in the center, you can undo it -- there's a screen underneath. Note that there is an indentation in the cap and a matching one on the pump body. It must go back together the way it came apart.

Not sure about how, or if, the later replacement pumps disassemble...

Put the filter between the pump and the hard line coming from the gas tank, not bwtween the pump and the carburetors. This will protect the pump, and you'll also be able to see what's coming out of the tank, not just what's getting through the pump screen.