One of the most recent version updates changed the default Agent Options to NOT allow deletion of backup storage using the agent console. This was done to prevent hackers from deleting backups during ransomwware attacks.
What we do when we need to delete items from storage is to go to Organization - Companies then edit the company select "Agent Options" then select "Use Custom options" and check "Enable ability to delete files from Storage".
Close and re-open the agent console and you will be able to delete files from backup storage.
Strongly recommend putting it back to default when you are done.