You can undo anything that you do in Microsoft Expression Blend if it results in a change to a file. For example, you can undo changes that you make on the artboard, and also changes in panels such as the Resources panel, because all those changes result in a modification to a .xaml or code-behind file in the solution. Some actions that you take might result in more than one change and thus are separated in the undo list.
On the Edit menu, click Undo.
Click Undo again to undo the action that you performed before that, and so on.
The Undo and Redo menu labels are appended with a description of the action that was last taken.
On the Edit menu, click Redo.
Click Redo again to redo the action that you undid before that, and so on.
Individual undo lists are maintained for each document until the document is closed. If the Undo and Redo commands are dimmed, there are no more actions to undo or redo.