Click on the Trim Tool option in the Draw Ribbon. Hover your mouse over the 2D element/part thereof you want to trim and if it gets highlighted, click on it to erase that part.

Click on the Extend Tool option in the Draw Ribbon. Hover your mouse over the 2D element/part thereof you want to extend to see if it automatically extends to a nearby point. If you are satisfied with the extension, click on the part you hovered over.