Choose Home tab→Modify group→Delete Faces 
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Select the faces you want to delete.
On the command bar, click the Accept (check mark) button.
On the command bar, click the Finish button.
Tip:
The faces and features you delete in the Simplify Model environment are added to the Simplify section of PathFinder.
You can use the commands on the shortcut menu to edit, delete, suppress, and rename the simplified features you define.
When you delete a face on the part body, which must always be a solid body, the gap is automatically closed. When you delete a face on a construction body, which is not required to be a solid body, you can specify whether the gap is closed or left open using the Heal option on the command bar.