If you would like to update an animated gif image and you don’t have the source file (PSD probably), you need to extract all frames from the gif image, update each frame and then assemble it back using Photoshop or other GIF animation software.
There are a couple of ways to extract frames from a GIF image:
1. Adobe flash
Use Adobe flash to open the gif file, all the frames will appear in the library.
Place the item from the library onto the main timeline, and do File->Export->Export Image
2. GIF Frame Extractor
GIF Frame Extractor is a free tool for Windows that lets you extract frames from any animated GIF and save them to JPG or PNG image formats instantly.
Run the tool, click Open and select the GIF animation whose frames you want to extract. You will see the number of frames on the left sidebar.
Select any frame that you want to extract and click Save. You can choose whether to save them in JPG or PNG format.