My O.S - Vista Ultimate

Question

My O.S - Vista Ultimate is installed in the C drive. Naturally the Windows automatic updates gets downloaded in the C drive. Today I find the C drive space (30 GB) is full. So the vital updates cannot be downloaded in the C drive due to lack of space. I have 70 GB free space in the D drive. How do I configure the drives so that I am able to download the updates normally on my computer?