I want to stop the premium version

Please go to your account > billing and select the free plan (downgrade) button:

Our plans have been restructured having new prices. This means that you can have access to the old price for as long as you keep the Premium plan active. If you downgrade now and later activate a subscription you will only be able to access the new prices. You can see here more details:

https://www.jotform.com/pricing 

Let us know if we can assist you further.