Undo/Redo
After making any change to you existing design, if you decide to revert back to the old design, you can perform Undo action. You also can redo the undo actions.
To perform undo action: click on the "undo" tool button, or Ctrl+Z
To perform redo action: click on the "redo" tool button, or Ctrl+Y
You can perform up to 5 levels of undo/redo .