Hi Stephanie Berry,
Please go through this Marketo Docs link : Delete a Workspace - Marketo Docs - Product Docs . Hope this helps you to solve your problem.
To delete a workspace you have to first unlink or unapprove all the assets which are active. After that you can delete the assets which are not required before deleting the workspace.
Thanks for confirming. I was hoping there was some hidden backend way to remove a workspace without having to do all of that, but it looks like that's the only option.