Here is how to make a file extension open with a specific program when clicked:

1. Right click on the file with the right extension you want changed like a GIF file.

2. Then click "Open with" and then "Change default program..."

3. Then select the program in the list or click Browes if it not there and add the program exe tot he list.

4. Make sure you check the "Always use the selected program to open this kind of file"

Now any time to click a file with that file extension, Windows will open it with the program you set here.