Reverting to a Previous Document State
Display the History panel, by choosing it from the Panels command on the View menu. The History panel appears, displaying a list of actions from earliest (top) to most recent (bottom).
Insert History Panel Graphic Here.
Select the position you want to move back to. The document reverts back to the point at which you made the change.
WARNING: Be absolutely certain that you want to revert to the document at the point you chose before performing any other actions. When you perform another action, the document history is cleared of all the post-reversion changes and the new action is recorded. It is not possible to then return to the pre-reversion state.