Confused about purchasing Full product

I am confused about purchasing the full product. Do I do it from my browser on my PC, download the product, then transfer it to my phone? Or do I somehow try to complete the web order page on my phone's little screen, and download directly to the phone? After reading some of the posts I decided not to buy the Lite version from the Market and try to figure out how to upgrade it.

 

(I have been using Norton on my PCs since 1989, but this is the first time for a phone.)

 

Thanks,

Gene