What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
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.
Unfortunately, I wasn't able to replicate the issue. I cloned your form and I was able to change the text without any problems. Please check the screen capture below:
As you can see above, I selected the field first and then click the "Edit HTML" button. After that, the editor will appear and I can edit the text. After editing it, I clicked the "Complete" button.
If you're still having issues, please try using another browser to check if it will work or not. I will clear your form cache so that your forms will be refreshed from our servers.
Hope that helps. Thank you.