Press Ctrl+Z on Windows or Command+Z on Mac
Press Ctrl+Alt+Z on Windows or Command+Option+Z on Mac to step backward through multiple actions
Use the History panel to select a previous state
Choose Edit > Undo from the menu
Use Edit > Step Backward to undo the last action
Use Edit > Step Forward to redo an action
Click the Undo button if it is available in your version of Photoshop