Not terribly hard. Loosen all the screw securing the inside trim, leave at least half loose but still attached.
Use a suitable tool to cut the silicon around the outside, something thin and kinda flexible, be careful not to scratch the paint.
Remove the inside screws while someone capable of lifting the window is outside ready to do just that. With the silicon cut and the inside trim removed nothing but age and habit is holding the window in.
Once it's out and on a solid surface you can disassemble it, clean everything, and replace the bad pane.
If it's an Atwood, their customer service is very good, and they can sell and ship you the replacement panes.