I have more than one LinkMachine account, and I have upgraded one of them. I would like to transfer all installations that use the other account to the upgraded account.

After logging in to a LinkMachine installation that you would like to transfer to a different account, go to Change Settings, Account Settings. On that page you will be able to change what LinkMachine account is associated with your LinkMachine installation. After entering your current password and clicking "Change Account" on this page, a page will appear asking whether you would like to log in using an existing LinkMachine account, or create a new one.