PHP update

I have downloaded the “Add From Server” plugin in order to link to our historical society stored data at EarthLink. When I activate our Add From Server I receive this error message: “This plugin requires WordPress 4.0 or greater, and PHP 5.4 or greater. You are currently running WordPress 4.7.1 and PHP 5.3.28. Please contact your website host or server administrator for more information. The plugin has been deactivated.” I have tried to update PHP, but have been unsuccessful. Could using an older version theme require an earlier PHP? Any thoughts or input would be appreciated.