As a precaution, you can perform the backup of the folders that contain portal data and logs.
C:\Program Files (x86)\Ascensio System SIA\CommunityServer\Data\
C:\Program Files (x86)\Ascensio System SIA\CommunityServer\Logs\
In case you plan to install ONLYOFFICE Workspace Enterprise Edition on a different server, or MySQL server is installed in a different location, you will need to create a backup of the MySQL database using any available software you have for such purposes. If only ONLYOFFICE is installed there, it is sufficient to copy the following folder.
C:\Program Files\MySQL\MySQL Server 8.0\data\
or C:\ProgramData\MySQL\MySQL Server 8.0\Data\
(depending on Windows version)
After all the data is backed up, please check the portal for correct launch and remember some user data to be able to check it after the upgrade.