JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
It might be something related to the browser, have you tried clearing your browser's cache and try logging back in. Make sure that you are logged in when upgrading your plan.
Here's how you can upgrade.
1. Log in to your JotForm account.
2. Navigate to account settings->Billing->Choose a plan.
If the page still freezes, could you try upgrading user a different browser? Maybe Chrome would do?
Do let us know if that works.