Help registering iMovie
I can't comment so I'll post in question format.

What version of mac osx do you have installed currently? How to find out in case you do not know:
Top left corner of screen with apple icon &gt; about this mac You should see the name of your OS and version number in there.
What version of mac osx did you just upgrade from. Is this the same machine or a different one? What backup software or method did you use if any.

Realistically you should probably be talking to whoever bought the application and Apple if you want to transfer ownership.

Worst case scenario, iMovie is $15… also, there are other options out there that are pretty good and cheap, some even free. A post on slant.co suggested Lightworks a hollywood approved film editor, Hitfilm 3 Express a video editor + compositor in one package, Kdenlive a GNU Linux initiative which could potentially be built using macports. I found a recommendation for Davinci Resolve on lifehacker on a random article about Superior Alternatives to Boring Stock Mac Apps. Their other pick as a replacement for imovie Screenflow 5 got terrible reviews (screencaster software, not dedicated video editor)