You can also activate the node title editor using the main menu:
(1) Click on a node (using your left mouse button) to select it.
(2) Click "Menu: Tree/Edit node name".
The node's name becomes an edit box.
(3) Type a new name or edit the existing node title.
(4) Press "Enter" to apply the changes (you can also press the "Esc" key to cancel the changes).