A workspace must first be archived before it can be deleted.
If your workspace is already archived, follow the instructions starting at number 4.
How to delete a workspace:
Select My Workspaces from the "Me" menu
Find the workspace from the active workspaces list
Click ... -menu on the right side and select Archive workspace
Select Archived workspaces from the top to view all archived workspace
Find the workspace from the archived workspaces list
Click ... -menu on the right side and select Delete workspace
Deleted workspaces cannot be restored, so think carefully about whether the workspace needs to be deleted or if it is enough to archive it.