Update paypal payment amount with choice of delivery

Trying to do a form showed a basic imput here if you choose Fax, email it costs $15.00 but if  you choose USPS mail it cost $18.00 how do I get the amount to change in the box below to $18.00 via paypal whenthey choose USPS mail ?

In this case, you may setup the products normally in the Payment wizard.

Then, you may setup conditions to display the required fields like email address or Fax number based on the selected product.

Please see the cloned version of your JotForm with the above changes. 

https://www.jotformpro.com/form/62588790262971?

Feel free to clone it to your account to see how it works.

Hope this information helps!  Please get back to us if you need any further assistance. We will be happy to assist. 

Here is the guide that can help you with cloning the form to your account.

https://www.jotform.com/help/42-How-to-Clone-an-Existing-Form-from-a-URL 

Thank you!