Go to the Uniden website, create an account and register your scanner. You will be able to download the Uniden Advanced System Director(UASD) from there. You will need to register anyway to get the firmware updates, and of course that's a horse of another color...
However I'd recommend getting FreeScan. It's freeware, allows you to download data from the database with a paid subscription, and has many more features (and better support) than the UASD. And now for some relevant links....
http://scannow.org
This describes the subscription plan....
http://www.radioreference.com/apps/subscription/
This wiki article has numerous links for the 396, including other software packages (including BCTool - not BCTools, which is a virus checker (lots of folks make that mistake) - which is also freeware), along with articles on DMA (the memory manager that the 396 uses...)
http://wiki.radioreference.com/index.php/BCD396T
73 Mike
