I invited a User to their Workspace at the wrong permission level. What do I do?

Go back into that Workspace.
click on Share.
in the list of the invited, find the User that is at the wrong Permission Level. (was probably set to Downloader)
in that Permission Level dropdown, select the proper Permission. (you probably want to set it to Creator)
hit the X at the top of the white Invite Modal (mid-screen, not the browser window).
Done.