If you have a file you don't need but you want to keep just in case, you can send it to your production's Archive:
Tap "Send to Archive"
You'll still be able to access these files by tapping "Archive" in the PML. If you want to restore the file(s), you can navigate to the Archive, select your files, and tap "Unarchive". They will retain any tags you attached prior to archiving, including any scenes or characters, so they'll reappear in their respective Moment Boxes (if applicable).
If you no longer need a file and want to remove it permanently from your production:
Follow the steps above to archive your file
Navigate to your Archive in the PML
Select your files and tap "Delete".
After confirming, the file will be permanently removed from the production. You cannot undo this action.