norton anti virus common files/symantec shared taking up too much space!!!

Hello - I keep getting low memory on my computer and investigation shows that c:program files/common files/symantec shared is taking up 24GB of my 30GB c drive!!! I've taken everything i can off my c drive but surely it shouldn't be taking up this much space.I understand that I shouldn't delete these files as they are virus defs.  I have plenty of space on d: drive.  Please help.  I have norton security 2006 which is updated each year.

 

Something of a basic user so the simpler the explanation the better 

 

Thanks