If you already have Metamill 6.x or 7.x license, you can upgrade your license to 8.1.
Make sure you have the license code available before purchasing the upgrade.
When activating with the upgrade license, you will be asked existing license code.
You can buy upgrade for any number of users. E.g. if you have now 5-user license, you can buy 10-user
license for the upgrade price. This is fixed license which does not expire.
Note: Upgrade is now possible for Windows and also for Linux license.
It is not possible for academic licenses.