You may undo or redo a feature edit step using the Undo or the Redo Feature Edit 
commands. These commands will Undo and Redo in a sequential manner within an edit session.
The Undo command functions at sub-feature and feature levels-
Sub-feature: As you edit at the sub-feature level (e.g. vertices), each operation is pushed on to the undo stack. If you press the undo tool, the most recent vertex edit operation will be undone. Once you click off the feature or press Save/Discard edits, the sub-feature undo stack is cleared and you can no longer undo at the vertex operation level. In fact, if you click off the feature and then press undo, all sub-feature edits that you have just performed will be undone as a group. Not to worry – you can restore them as a group by pressing the redo tool.
Feature: Anytime you click off a feature, the sub-feature undo stack is cleared. Undo will now undo at the entire feature level.
The Redo command reverses the most recent feature or sub-feature undo.
Click on either the Undo or the Redo Feature Edit commands on the Feature Edit Tab.