Un-do using History feature
Dreamweaver

One of the most useful new features in Dreamweaver 3.0 is the History window. If you are familiar with PhotoShop you are probably familiar with the History feature.

Within this window, each action you have performed since opening your document is listed, so you can keep track of your actions and easily undo or repeat your last step.

Simply highlight the last step in the History window and hit your Delete key, or drag the sliding indicator up the list of steps to delete several steps at once.

You can also click the window's Replay button to perform the step again.

The default number of steps is 50? To increase it, select Edit/Preferences, make sure you're on the General tab, and enter a higher number in the "Maximum Number of History Steps" field.  

NOTE:: The more steps you want to save, the more memory you'll use.