finally, I played with turbotax and find a way to delete a form (the instructions that on TurboTax's web site doesn't work for Mac version)
1. click big "Form" icon at top-left corner
2. a list of form will be listed at left panel
3. select the one you want to delete (in my case there was a empty home office worksheet accidentally added somehow, but not visible on "EasyStep" view.
4. press "delete" button on your Mac (nothing on the menu, no right-click popup menu)
