This can be handled in a few ways. For retired content if you are looking to remove those from the CMS, the recommendation is a timeout transition in the workflow. This is done within the workflow where you can set a transition from Retired to Archived and similarly Archived to Deleted after a period of time. A common setting is retired to archived after 30 days and retired to deleted after another 30 days. This way you don't have to manually remove the files.
For the orphan files you will need to run an orphan report for the particular site to identify items that are Live but are not accessible/linked from any pages. Then from that report you can identify how you wish to handle those orphans. Since links are generated dynamically this is the easiest way to identify them. Orphan reports are available under Reports, Audit, Orphan reports.