Permissions Problem

I am needing to clear some space on my (10 year old) Drobo S but I am unable to delete files and directories. I receive a message that I need administrator access. This happens even though I am logged on with administrator access and do have administrator access to the files and directories.

I would be grateful and impressed if someone could suggest a quick solution but I presume I will need to wipe everything and start again, regenerating all backups. In this case, in Drobo Tools, should I select Format or Erase & Factory Reset?