Upgrading to v4
Upgrade to version 4.x from 3.x requires upgrade of both server and client sides. Older clients will not work with new servers and vice versa.
Upgrading servers based on MongoDB
Go to admin/status page and check for updates, the process is fully automated. To be on a safe side - backup a copy of /conf folder before upgrading. The update process will adjust your existing configuration and will take few seconds to complete.
Upgrading servers based on relational databases
To be on a safe side - backup a copy of /conf folder before upgrading. Database schema was extended in this release to contain five more MDC columns (mdc6 - mdc10). One way of updating is from admin/status page, database schema will be updated automatically during the installation. Note that with large databases (millions of rows) adding new columns will take time (depending on database), so be patient and select appropriate time for the update. Alternatively, you can manually add new columns (mdc6 - mdc10) to your database and then start the update from admin. Let us know if there are problems.
Clients need to be manually downloaded and re-installed on top of existing installation, or at a separate location if you still use v3.