If you have an existing limited site license for a LifterLMS add-on, you can get prorated so you get a discount while upgrading to an unlimited license (Infinity Bundle).
To upgrade yourself to an Infinity Bundle with unlimited licenses, log into your account here on the LifterLMS website and press the orange Upgrade License button on your subscription.
Then add the Infinity Bundle to your cart. The sign-up fee shown in the cart is the cost to upgrade between the time you do the upgrade and the next renewal date for your subscription. If you run into any questions or concerns during the process please email us at team[at]LifterLMS.com.