You can add more packs to your license, or add more sites / seats to a pack, by ordering a subscription upgrade.
Open your subscription (aka license) Login to your account
Open the upgrade order form
Set a # of sites / seats for each of your pack
You will receive shortly an upgrade confirmation email from Avangate, our order processor. When you do, you can connect to your WPSOLR account, open your subscription, and verify that the new packs and their number of sites are updated.