Can I upgrade for a few months?

Im running a contest on my website for 1 month. Im worried ill go over on submissions. I dont want to lose entries but just need to upgrade for 1 or 2 months tgen go back down. Is that possible?

Yes you can, here's a guide on how to upgrade: https://www.jotform.com/help/331-How-to-Upgrade-My-Account. You can choose monthly, yearly or bi-yearly plans. In your case, you need to select monthly plan. You will then be billed on a monthly basis. To stop your subscription, simply downgrade back to "Free" plan before the next billing date. 

To downgrade back to "Free" plan, you can follow this guide: https://www.jotform.com/help/341-How-to-Downgrade-Subscription-Back-to-Free-Account 

I hope that helps.