Undo and Redo (Edit Menu) CTRL+Z and CTRL+Y
Undo
Any changes you make to a document can be undone. The recorded undo information is not saved with the document and so, if you save a document and later reload it you will no longer be able to undo changes you made before the Save.
Redo
At any time when you have Undone some changes you can choose to redo them again. This is very useful because it gives you the ability to change your mind about an edit as many times as you like.
Undo and Redo always show a brief description of what will be undone or redone. For example "Undo Delete".
Tips
Except when using the Text Tool, you can also use the < and > keys to Undo and Redo.
The number of steps you can undo depends on the memory that was available to record them (see Tune-ups Options).