Thanks, that did the trick.
I used EasyApache 4 (on WHM) to install PHP 7, and then cPanel (on the site) to enable PHP 7 for that site.
Now I have to update a bunch of stuff to get it all working.
General help
Upgrading from 3.0 to 3.5; how to point to PHP 5.6.5?
This discussion has been locked so you can no longer reply to it.