When clients are removed from a source machine, all backups are also deleted from the source; however, replicated backups remain. This can cause the capacity of target system to be reached even if there is extra capacity on the source unit.
From the legacy UI, open up the navigation options/system preferences at the bottom of the navigation pane by clicking the gear icon:
Check the option "Show Replication View?" and then click confirm. In this view, you are modifying replicated backups instead of controlling other Unitrends appliances remotely.
Select the client you wish to delete backups from in the navigation pane.
Next, navigate to the backup browser
Settings -> Storage and Retention -> Backup Browser
Choose the time period to select backups from (eg. "All time) at the bottom of the screen.
You can then select one or more backups to delete.
Note: Replicated backups are stored in deduplicated format as SIS data. Whereas removing a client from the source system will free up space almost immediately, it can take quite some time for backups to unhash and free up space from a replication target.