I logged in and can't seem to locate a place to enter payment

I received this email  : 

Dear jane4701, 

We have been unable to collect the payment for your subscription. 

To keep your account active please log in to your account and update your billing details within the next 7 days or your subscription will be cancelled. 
------------------------------------------------- 
SUBSCRIPTION INVOICE - 2017-10-29 
Email: jlind801@gmail.com 
Plan: Bronze 
Amount Due: 19.00 (USD) 
This covers usage between 2017-10-29 and 2017-11-29 
------------------------------------------------- 
Thank you 
JotForm Team 
http://www.jotform.com/

I logged in and can't seem to locate a place to enter payment. 

Another question is I feel I need to down grade my subscription but the site won't allow me to do this . Where can I accomplish this task?

You have to account your billing section.

My Account > Settings > Billing

https://www.jotform.com/myaccount/settings 

https://www.jotform.com/help/341-How-to-Downgrade-Subscription-back-to-Free-Account