Can I just install this upgrade over 20/10 version or do I have to change or add anything beforehand?
22/12A (Legacy Edition) is a derived from the 20/10A distribution codebase for the latest PHP version support with a feature roll-back approximately equivalent to 14/06A. Please see the changelog for more details. This is intended to be able to continue to offer the script for sale whilst removing the most complex and least used features therefore making the script significantly easier to support.
Maintenance updates for 20/10A will continue to be provided as required, but for new projects if the deprecated features are not required then I would suggest getting started with 22/12A...