add webroot to the second computer: to add Webroot to another computer first of all you need to have a license for more than one system. Now if you have one simply login to your Webroot account there you can add or remove any system. After adding you can download the program for that system.
In case you have a one user license then you can install it on only one system. Login to Webroot account on that device where you want to add Webroot. So you can download after adding that device to the Webroot account.