There are three ways to delete a workspace:
Click on the workspace tab you wish to delete. This opens the workspace.
Click the "X"
at the bottom of the application where the workspace tabs are located.

OR
Position your cursor on the workspace tab you wish to delete.
Right-click
to display the context menu, and select Delete
Workspace.

OR
Click on the workspace tab you wish to delete. This opens the workspace.
From the Edit menu, select Delete Workspace.
Note: Depending on your Account Preferences, you may be asked to confirm that you wish to delete the workspace.