How can I fix my casement windows?
First I will answer the question. Remove the window and reinstall it. You may need to adjust the lower sill or cut a little out of the header at the top to get it to set level. It is a non bearing wall so a 1/2" off the header will not matter. The sill will not have any extra material to cut out. Or you could simply resquare the window and let it run downhill like it already is.

You will not be able to trim any of the window sash to get it to fit back in without destroying the vinyl cladding, so it has to be reset.

Now for the real issue. The picture does not reveal any other symptoms but I will tell you what I see going on with the window

The wall to the left has settled for some reason, if it was originally a porch and not a living space, it may have not been structured the way a living space is needed. Either the footings where not sized properly and the footer settled down some or perhaps termites or carpenter ants got in there and caused some settling.

I would consider doing something with that, and it may not crack the window on it way back up, but when the window is corrected it will stay.