If you are experiencing issues when editing your subscription, do the following:
Clear the cache and cookies of your browser. To see how to clear your cache and cookies click on this link: https://support.pipedrive.com/en/article/how-do-i-clear-my-browser-s-cache-and-cookies
Test to see if the issue persists in an incognito window and other browsers.
Check if you have an overdue invoice or a declined transaction.
Check that your most recent invoices have been paid and, if they have not, you will need to pay your unpaid invoices before editing your subscription. To learn how to check your past invoices, click on this link: https://support.pipedrive.com/article/how-can-i-view-my-past-pipedrive-invoices