Adding desktops in Kubuntu 14.04
1. Start button
2. System Settings
3. Workspace Behaviour
4. Virtual desktops
5. Enter the number you want in the "Number of desktops" bar.

To edit keyboard shortcuts related to the desktops, use the "Switching" tab.
Then edit the Shortcuts as desired.  (Be sure to click on the "Apply" button
on the lower right-hand corner after any changes you make.)