try this site out: link it has a pretty elaborate image editor that works right there on the site and it will also give 你 a walkthrough of it if 你 get confused about anything!
I usually do stuff with GIMP... It's pretty good for free software. Advanced and technical, but good, especially when 你 learn how to use it. There's a lot of tutorials on Youtube, and if 你 can't find what you're looking for there, just ask me XD