Web developer required ASAP - 'theme is loading an out of date version of jQuery'

Hi there, I am working on a wordpress site for a client which has WP Simple Pay Pro plugin installed which was working until some changes were made to the site (basic log of recent work available). There seems to be an issue with the reCAPTCHA. After contacting WP Simple Pay Pro support I was told the following: "It appears that your theme is loading an out of date version of jQuery: <script type='text/javascript' src='[login to view URL]'></script> This is causing AJAX requests to the WordPress API to fail because it's sending the form data via the URL vs. a POST request, causing it to fail. You will need to contact the theme author to disable the additional version of jQuery that is being loaded that is causing the AJAX requests by WP Simple Pay to fail." I need someone who can help me resolve this issue and ensure that payments can be collected using the WP Simple Pay Pro forms. Thank you in advance.