To remove the 24mm nut and strainer, you need to remove the oil line from the right side bottom of the case. This will allow you to work the hose loose from the nipple on the bottom of the frame. Once you get this off you can put 24mm socket with long ratchet, or a pipe on a short ratchet, and it comes right off.
Now the question: Is this necessary? Probably not, but the key word here is probably. There will probably not be anything at all in the screen strainer but you won't know for sure unless you check it.
I checked mine once after about a year of riding, kept meaning to check it sooner, and it had absolutely nothing in it. So I cleaned it anyway and put it back. I will probably never check it again.