How Can I Clear Out My Art Library After Downgrading From Pro?

After downgrading my account from Pro, I'm unable to upload anything at all until I clear out the gigabytes of content I uploaded over the years with my Pro account.  Surely I'm not expected to delete each item piecemeal, or even page-by-page --- is there a "burn it all" button I can click somewhere? 

There is no burn it all button, sadly, at least not one I'm aware of. You probably already know this, since you mentiioned "page by page," but for reference for anyone reading this, you can click on any image in Recent Uploads to open up Folder View, and from there you can select multiple items to delete them all at once. Also (again, mostly for reference for people reading the thread), if you have uploaded any audio files, that's a good place to start when freeing up space. Go to Jukebox, then Manage Audio, and, in the My Audio tab, click on the title of a track to enter edit mode, then click the trash icon to delete it. Wish I had better advice. Improving ease of file management has been one of the more popular suggestions on the forums. Edit: Yay! I'm glad something I said turned out to be useful. If you'll forgive the D&D 5e metaphor: certain tasks on Roll20 are gated behind DC 18 Arcana checks, so I'm happy to perfrom the Help action when I can.

Go to Jukebox, then Manage Audio, and, in the My Audio tab, click on the title of a track to enter edit mode, then click the trash icon to delete it. You're my new hero; I figured out how to (reasonably) quickly Select All -> Delete my art assets, but it was the music tracks taking up the lion's share of the space ... but I couldn't figure out how to delete them.  Thank you for the preemptive advice, this is a responsive forum! ;)