Not going to happen. Almost positive that Lenovo is like any of the other computer manufacturers (Dell, HP, etc) in that they remove/hide any and all options in the bios that would allow for overclocking.
Another thing to consider is that you don't really have a desktop,
Lenovo - Desktops - IdeaCentre B510 23" All-in-One PCs
essentially it is nothing more than a laptop built into a monitor, and have all the same problems with cooling (if not worse) as a laptop would if overclocked.