If you purchased the Single Plan or Plus Plan, you're limited to the use of WP Rocket on maximum of one or three websites respectively. But if you need to use WP Rocket on more websites, you will need to upgrade to the Infinite Plan. All you have to do is pay the difference in price between the Infinite Plan and your current WP Rocket plan to upgrade. Note that this upgrade does not extend your current WP Rocket license expiration date.