Mistakes happen. When you draw something you didn't mean to or change your mind after an editing procedure, Paint lets you gracefully take one, two, or even three steps back.
To undo your last action in Paint, choose Undo from the Edit menu. To undo your second-to-last action, choose Undo again. Choose Undo a third time to undo your third-to-last action.
Paint is so forgiving, it even lets you change your mind after you use Undo. You can restore any actions you changed with Undo by choosing Repeat from the Edit menu.
Just as with Undo, you can repeat up to three actions.
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The keyboard shortcut for Undo is Ctrl+Z. Just like choosing Undo from the Edit menu, you can press Ctrl+Z up to three times to undo up to three actions. The keyboard shortcut for Repeat is Ctrl+Y.