The question is asking how to upgrade Discus 4.26 to Mac OS version 11.5. However, it seems there might be a misunderstanding as Discus is a program for Windows, and upgrading it to a different operating system like Mac OS is not possible.
To buy Discus in the Windows (10) version for Europe, you can visit the official website of the Discus software and look for purchasing options specific to Europe.
The question is asking how to upgrade Discus 4.26 to Mac OS version 11.5. However, it seems there might be a misunderstanding as Discus is a program for Windows, and upgrading it to a different operating system like Mac OS is not possible.
To buy Discus in the Windows (10) version for Europe, you can visit the official website of the Discus software and look for purchasing options specific to Europe.