The suggested update will delete your configuration.
I would first advise to download a Backup archive of your current configuration from System -> Backup. Having a backup will allow you to revert to earlier firmware and restore current configuration.
Next, try the custom script option first.
If it does not help, update your device's firmware to the latest with Keep settings option set to on. This will carry configuration settings with the update. However, keep in mind that due to there being many changes in 7.3, your configuration may not migrate correctly and you may need to reset your device and reconfigure it from scratch. You should be allowed to upload a backup from previous version.
Otherwise, having a backup may simplify reconfiguring task, by copying configuration files from backup's /etc/config directory to router's via scp/WinSCP.
Best regards,