Minimum PHP Requirements
As of version 1.9, WP Migrate DB Pro requires PHP version 5.4 or higher to function. In general, it’s always a good development practice to run the latest stable version of PHP.
To update PHP to the latest stable version for your WordPress site, your best bet is to contact your web hosting provider. Managed hosts like WP Engine, Dreamhost GoDaddy etc. should already be running a stable, newer version of PHP.
WordPress recommends running PHP 7.2 even though PHP 5.2 is technically supported. A good overview of how to upgrade PHP can be found here