You can undo and redo steps by clicking Undo and Redo at the top of the Equations dialog box.
Undo 
and Redo 
are available in all views. You can undo and redo any edits that you perform since invoking the dialog box.
If you change configurations while in the Equations dialog box, Undo and Redo lists are reset. Prior steps cannot be undone or redone.