In the Planning app, Admins can manage all their Planning cloud storage files on the Cloud Storage page. To get to this page, click your name in the upper right corner (or the gear icon on the mobile app) and select "Cloud Storage."
On the Cloud Storage page, you will see a list of all the files that have been attached to various Planning songs and services. These can include PDFs, images, Word documents, etc. If you're running low on cloud storage space, you can delete items in bulk from this page. Simply check the box for the items you no longer need and hit the Delete button in the upper right corner of the list.