Presentations has a very practical feature: You can use the command Undo 
in the Quick access toolbar to undo the most recent changes made to a document. If, for example, you format text in a different font and then don't like it, all you have to do is choose the command Undo and it will be undone again.
This not only works for formatting, but for virtually all changes – for example, you can undo typing or the deletion of text.
The command Undo can be applied repeatedly if necessary. For example, you can choose it five times to reverse the last five changes. (Tip: You can set the maximum number of actions that can be reversed in the Settings, General tab.)
If you click on the small arrow next to the Undo button, you will see a list of recent changes to which you can revert. If you click on an entry in the list, several steps can be undone at the same time.
Redoing undone actions
There is also a counterpart to the command Undo: the Redo button 
on the Quick access toolbar. This restores the last action you undid. You can thus undo the cancellation of text changes.
This command can also be chosen several times in succession. If, for example, you choose the command Undo five times, the last five text changes will be undone. If you then choose the command Redo five times, you will restore the original text.
Again, you can use the small arrow next to the Redo button to select entries from the list of recent actions to restore multiple steps at the same time.