How to delete security certificate?

My  tilt 2 is have issues automatically syncing with my company's Exchange 2007 server.  I looked under Start - system - certificate and saw that the root security certficate expired 1/7/10.  I think this may be the culprit.  However, when I "tap and hold"  the delete option is not available.  How do I remove it?

Thanks in advance,

W!