To force an Update from a WSUS Server:

From the command line, type the following:

C:>Wuauclt /a /detectnow
C:>Wuauclt /r

The CPU will now go up to 100% utilization for a few minutes, once it settles down you should see the wuauclt.exe process if it's working.

The switches do the following;

/a or /ResetAuthorisation indications an asynchronous background search of applicable updates.
/r or /ReportNow sends all queued reporting events to the server.