See detailed upgrade instructions for a more in-depth explanation of the upgrade.
Download latest NiDB release.
yum --nogpgcheck localinstall nidb-xxxx.xx.xx-1.el8.x86_64.rpm
Make sure your IP address is set in the [setupips] variable in the config file. This can be done manually by editing /nidb/nidb.cfg or by going to Admin → Settings
Go to http://localhost/setup.php (Or within NiDB, go to Admin → Setup/upgrade)
Follow the instructions on the webpages to complete the upgrade