How can I upgrade for just one month?

how can I upgrade for just one month

To upgrade for a month you should upgrade with any of the monthly plans you like. Then you can downgrade once it is close to the next billing date.

To upgrade the account please refer to this guide:

https://www.jotform.com/help/331-How-to-Upgrade-My-Account

To cancel the subscription and downgrade to free refer to this guide:

https://www.jotform.com/help/341-How-to-Cancel-a-Subscription-and-Downgrade-Back-to-Free

Let us know if you have further questions.

Thanks.