Can't Edit GIF file in Photoshop?

It's a hard to edit GIF file in adobe Photoshop, it's locked and can't do a thing to it. If u tried to save it as a PSD and a TIF, the same thing will happens. It's locked. If u tried to go into the image properties to see if "Read Only" was checked, but it's the same result, fail!.
So, u can do this trick to open and edit Gif file in adobe photoshop. Follow this step:

1. Open the GIF image in Photoshop.
2. The problem is that the .gif file is in "Indexed Color" mode. then
3. Change the Image/Mode to RGB Color and you should be able to edit it. The methods are click top menu Image > Mode > choose RGB Color.
4. This is it, u can edit, add and customize the picture.
5. If u want to save in gif image, u can click File > Save for web.

NB:
U can read similar information on http://www.retouchpro.com/forums/image-help/16199-cant-edit-gif-file-photoshop.html.
http://answers.yahoo.com/question/index?qid=20080614101841AA2fhCj