Firmware upgrade failed due lack of HDD space

Hi.

When trying to upgrade my iPhone 4 firmware, iTunes 10.1 reported ...

"the disk you are attempting to use is full"

Disk C:\ was full. I believe that iTunes stores the just downloaded firmware somewhere in a temp folder and extracts data ther later on.

How cam I change the location of this folder?

Yes ... I can empty C:\, but nevertheless I'd like to know how to change the path.

Thanks,