... Also, just to be clear, you only need to install 10 once the first time you register (and pay for) v11. This is just to allow you to "upgrade" from inside v10 which gives you the special upgrade price.
A small fix:
"This is just to allow you to "upgrade" from inside
v11 which gives you the special upgrade price."
Once again:
1. MC10 must be registered.
2. You can uninstall MC10 before installing MC11. Just make sure that you have backed up your library and the cover art folder. I think this is the best way, but it's just my opinion. This step is not needed or recommend by JRiver.
3. Install MC11.
4. Inside MC11 click the Buy button for starting the purchase.
Edit
If you are going to uninstall MC10, you don't need to let MC11 scan your HDs for the media files (MC will open the import dialog if the library is empty). Instead you can just restore the MC10 library backup file to MC11. It will then restore also playlists, playcounts, etc.