pptXTREME 2015 can be installed independently of earlier versions and they can co-exist if you so choose.
To uninstall pre-2105 versions:
1. Open Programs and Features by clicking the Start button Picture of the Start button, clicking Control Panel, clicking Programs, and then clicking Programs and Features.
2. Select each legacy pptXTREME product, and then click Uninstall.
To install 2015 (and above) products, follow the instructions in the help section.