A downgrade is technically not possible because your user account will be permanently adapted to include the extended functions of the license you have purchased.
A downgrade could have fatal consequences and, in the worst case, result in you no longer having access to your data and documents (user rights, operation on NAS, etc.)
Tip: Alternatively, create a new user account and then port the PaperOffice database. Note that certain license types such as PaperOffice FREE cannot access NAS.