I don't know if you might find helpful advice in the photography forum?
https://icraftgifts.com/forum/b15/photography-advice/Not sure if this is helpful about sizes:
https://icraftgifts.com/forum/1095/photo-sizing/1/I use a free program called GIMP to edit my photos. There are others out there though. It's hard to edit upwards and still have a crisp photo though.