You can upgrade/migrate from older to newer versions, but when you have done this the data will be incompatible to previous versions (maybe updates work, but not main releases and service packs)

also only upgrades for licenses

Hello,

You may use a WinCC 8.1 license with a WinCC 7.5 installation. The license is backward compatible this way. You just have to possess the 7.5 install software if you want to use 7.5. Once a license is upgraded, it is not able to rolled back to the old version by the user. However, there is no need for this because it is compatible.

Thanks,

Steve