I've looked all over but have yet to find a good tutorial on how to edit an existing GIF I've found on the web. What is the best way to take an existing animated GIF and add text or images on it in CS6? BTW there are lots of tutorials on how to create a gif from scratch from a video but they don't help on editing an existing GIF.
Seems like you should be able to edit a gif the same way you create one. I just opened a gif I pulled off the web, and opened it in PS. All the frames were shown as layers. I could then click on any of the layers or frames in the frame animation pane and update edit them. In the pop up menu on the timeline you can select "New Layers Visible in All Frames" if you want to add text that will show in all the gif frames or you can editing one by one by unchecking that selection. Have you tried editing a gif, and what issues are you having?