You can undo any changes or redo them if you change your mind.
Undo the last action: Choose Edit > Undo (from the Edit menu at the top of your computer screen), or press Command-Z.
Redo the last action you undid: Choose Edit > Redo (from the Edit menu at the top of your computer screen), or press Command-Shift-Z.
If you don’t want to keep a document you haven’t saved yet, close the document, then click Delete in the save dialog.
If you open an existing document, edit it, then decide you don’t want to keep any of your changes, you can revert the document to its state when you opened it.