Want to seek advice that if perform backup for 3CX system v12, uninstall it, and install 3CX system v14. After that, restore back the backup data to v14, is that workable?
You mean I need to upgrade current v12 to sp 6.2 first and later perform backup database? After that uninstall v12, install v14 and restore back database and it would work fine?
Yes you need to be to service pack 6.2 to be able to upgrade to v14 directly.
Once you have service pack 6.2 you can perform a backup through the 3cx backup tool uninstall v12, restart your machine, install v14 and apply your backup.