Choose the Delete Rounds command 
.
Select the rounds you want to delete.
On the command bar, click the Accept (check mark) button.
On the command bar, click the Finish button.
Tip:
You can use the Select option on the command bar to specify whether you want to delete faces or features.
You can delete rounds on the design model or you can delete rounds to create a simplified version of the model in the Simplify Model environment.
The faces and features you delete in the Simplify Model environment are added to the Simplify section on the PathFinder tab.
You can use the commands on the shortcut menu to edit, suppress, and rename the simplified features you define.