Have you registered your amp?
If so, go to your Line 6 account and select "Purchase History" under Hardware & Software.
You should see a line saying "Cubase LE" under items with a "details" link.
You'll be provided a download access code to use at MySteinberg.
Click on "Create account" if you don't already have one and then provide the download code in the "Register eLicenser / Sofware & Enter Download Access Code" field.
You'll then unlock and receive a separate "activation code" from Steinberg to use.
If you haven't registered your amp, do that soon.