Several web hosts offer the ability to change your version of PHP through the cpanel / hosting panel area. Try searching their support area to see if that is available.
If it isn't, then here is a message that you can share with your web host in a support ticket. Be sure to change example.com to your actual website URL.
Hello! I’m using an ecommerce plugin called Event Espresso on my WordPress site:
example.com
My WordPress site is using an older version of PHP. Could you please help me switch my site to a current version of PHP?
Thank you!
Our recommended WordPress hosts all support a current version of PHP: https://eventespresso.com/requirements/
References:
http://eventespresso.com/wiki/braintree-payment-gateway/
https://eventespresso.com/topic/gateways-using-braintree/
https://eventespresso.com/topic/braintree-support-3/
https://eventespresso.com/topic/braintree-support-2/
https://eventespresso.com/topic/mijireh-gateway/
https://eventespresso.com/topic/new-zealand-payment-gateways-source-code/