[Dedas]

If you want to delete the information from the registry do this:
1. Press "Start"
2. Click "Run"
3. Type "regedit" and press enter. The registry should reveal itself to you.
4. Press F3.
5. Type Ubisoft and press enter.
6. You should be presented with a folder named Ubisoft. If not press F3 again.
7. Under the Ubisoft folder you should find a subfolder named Homm5 or the like.
7. Delete the Homm5 folder.

You are done. Ubisoft do not write much more to the registry than this. At least not to my experience.

There are also programs that could do this (delete unused registry entries) but this is how you do it manually.