If you need to edit a note as a whole, not by its individual lines, you can click on the button right to its name:
edit-note-button.png
 
This way the note will be saved when the editor loses focus (you switch to another window or tab, for example).
 
If you need to edit note without autosaving it on these events, you can click on "Text" menu item in the note menu:
note-menu-text.png