1. Add One Time Purchase Credits to get you through until your subscription renews.
2. Cancel the Current Preapproved Payment Agreement you have in your paypal account and then add a new subscription (basically, that's like starting over with your credits early)
3. Add Another Subscription and still keep your current. If you want to do this, you'd keep your current subscription and just add another. You'd be running more than 1 recurring subscription until you choose to cancel one.
Some helpful videos are below.
1. How to Estimate Credit Usage and Choose the Right Plan - https://www.youtube.com/watch?v=3bK5w_cWZEM
2. How to Cancel Your Sku Grid Subscription - https://www.youtube.com/watch?v=u4zhcu6aP1g&list=PL1P6jkYBkBWFw0kMqBA8aSsmDJ2VGZic4&index=9
3. How to Add a Subscription - https://www.youtube.com/watch?v=Je1g3JgkkYc&list=PL1P6jkYBkBWFw0kMqBA8aSsmDJ2VGZic4&index=8