UrBackup is generally quite efficient if you have started with a good amount of backup space and proper settings. Changing the backup storage can be done, but you need to be sure you really need more space and not just better use of the existing space or you will be doing this again and again.
First, be sure you have set the Global soft file system quota appropriately for your environment. (8.1.14 in the Administration Manual) 90% is a good starting point for many systems, 95% is OK if you have more than 8TB of backup storage. This should be set as high as possible, but not so high that individual backups fail between automatic cleanup or Windows gets into trouble from running out of space.
Second, verify your backup selections are set to only what needs to be backed up, and does not include temporary files or automatically downloaded updates such as virus definitions. UrBackup uses Windows list of files to exclude as much as possible, but this generic list does not know about your specific needs. Add unneeded folders to the default or client exclude list.
Third, run cleanup.bat from the UrBackup Server program directory and check app.log for errors and reasons it could not delete old backups from specific clients. Use that information to adjust the Minimum number of … backups in Client Settings to keep fewer copies, especially of image backups which may not benefit from deduplication under Windows.
Lastly, if you can use Windows to enlarge the backup drive or third-party tools to copy the backup disk to a larger one, and can keep the same (8.1.1) Backup storage path, then UrBackup will automatically make use of the added space.
If you need to change the backup location, see Section 10.8 to migrate backup storage to a different drive. Look in this forum for that topic as additional details are discussed.