Canon New F1 focus screen change

Here’s a PDF of the owners manual which gets into the different viewfinders and focus screens Canone F1n owners manual

Jump to page 48 which gets into the details of metering with the different screens.

Jump to page 55 to see how the viewfinder is removed by pressing the two release buttons on it and sliding it out the back. It doesn’t take much effort, if it does you may need to use a little cleaner on a cotton swab to clean off the junk with is jamming it up don’t use to much! Once the finder is off, carefully grab the back edge of the screen to lift it out.