The easiest way to perform an Undo in Photoshop is through the Edit tab. In order to perform an Undo, simply access the Edit tab and the Undo option will be the first one on the list. The short code for the Undo is Command Z.
Contrary to other Adobe software like Illustrator and InDesign, Photoshop only allows 1 Edit undo. But Photoshop also allows more Undos through the History panel. If the History panel isn’t already showing on your desktop, simply access the Window tab and choose History. The History panel will allow you to go back X number of steps or actions.
How to use History function:
• Open the History panel from the window tab in at the top of your Photoshop window
• You will now have access to the number of actions enabled in your preferences
• From here, you go back in your history and choose where to resume your work
• Note that this only only possible for the work session. When closing your document, your history will be reset to zero.
You can also change the number of History actions you have control over. The maximum number is 1000.
To change the number of History actions:
• Go to Photoshop Preferences
• Go to Performance
• Once in Performance, access the History State box which allows you to change the number of actions
• Note that higher the number of ‘states’ selected, the slower Photoshop will become as it needs to store these actions on your disk. We recommend no more than 100 states.