To Delete a Tool

In the Customize dialog ( File > Settings > Configuration > Customize ) , click the Tools tab.
Expand the User Tools section and expand the open DGN file.
Expand the toolbox containing the tool that you want to delete.
Select the tool that you want to delete.
Do one of the following:

Click the Delete icon.

or
Right-click the tool and select Delete from the pop-up menu.

or
Press the <Delete> key.