You can't simply update the connection. All of the pages would have to be manually updated to MySQLi as well. This would not be a simple process. We are working on an update to PowerCMS for MySQLi. In the meantime you should be able to run on php 5.6 without updating to MySQLi. I would work on that instead of trying to update to MySQLi, since that would be a very difficult process on your own without extensive php hand coding experience.