Here are a couple of pics of the filter out of the bike
Front view and open
Back view
Removing the screws with the right tools as suggested is correct. You can run into trouble fast if you bugger up the heads.
Scrape and clean the "filter" with WD-40 or the like.
I get radical about the oil suggestions.
I won't use anything but Shell Rotilla Straight 30 WT DIESEL OIL. Why?
Diesel oil still has the Zinc anti-scrub additive in it. Modern oils have very little or none of this additive. Your old engine has a direct contact cam to valve end "valve train". The additive above keeps that old system working as designed.
Another reason for not running multi-weight oil in old air cooled engine is that the heat produced will break down the wax additive that enables the "multi-weight feature" in such oils.
I came to terms with the above subject by siezing my newly rebuilt CA95 engine using high end synthetic multi-weight motorcycle oil at $10.00 a quart.
I got a huge lecture from my friend with a doctoral degree in petroleum science. I got chewed by a long time friend who rides older bikes and then I did some research of my own. If you want to verify my words google" API Ratings" and read for yourself.
Get the Diesel oil at your local Tractor Supply Store. $12.00 per Gallon.
Your bike takes 750 ml of oil when the oil filter is not drained. It takes a full 900 ml when fully serviced. A quart of oil is 846ml. When you check the oil, don't screw in the dip stick to measure. Always check the oil after a short ride.
I use a nice glass measuring cup for this task.