If you reach your plan's design limit, you have a couple of options.
Firstly, you can consider upgrading to a higher monthly limit, which can provide you with more room to create new designs as your needs grow. When you scale up, you can benefit from a lower price per design image. However, please note that design images do not carry over to the following month.
Alternatively, if you don't want to upgrade, you can wait until your credits renew at the beginning of your next billing cycle. This will give you a fresh batch of designs to use without having to upgrade your plan.