Dear User,
Have you tried closing Elements 2016 and then installing the new Premeier Elements 2020.
Also, are you using a DVD for installing the upgraded Premeier Elements 2020.
You may try installing with an installer file.
Steps to install using an installer file :
1. Goto https://www.adobe.com/products/premiere-elements/download-trial/try.html#
2. Click on Download Adobe Premiere Elements 2020.
3. Select "Mac | English" (Here English would be the language in which you intend to use the application)
4. Click on "Download Now"
5. "PremiereElements_2020_WWEFDJ.dmg" file would be downloaded onto your system.
6. Double click on the file to mount it, and then follow the installation process.
Hope this helps resolve your query.
In case if you have any other query, Please let me know.
Regards,
Divy Jain