off line fark request

I cannot seem to get the hang of any of the animated gif editing tools (free) out there. Trying to get the heads of some of high up co-workers on another animated gif. But don't want to have it posted on line. ANy takers to put replace the head shots from the original animated gif (already animated) with the faces from 4our regular gifs, so that the original animation wil now have their heads on it?