Deleting Custom Cover Page

You can't delete a cover page outright, but you can replace your current cover page with a blank one.

To do that, navigate to your Proposal Settings (Under the Gear icon). Then, go down to "Add Additional Files."

Type "Blank Cover" in the Add File section. 

Choose the "Cover Page" header, and hit Submit without uploading any file. This will clear out whatever you have set up currently.