Basic PHP should already be enabled. However if you need certain addons such as the GD Library then you'd need to upgrade to the intermediate PHP package.
If you go to http://www.x10hosting.com/home and sign in you are taken to your account page. Here you can request a higher version of php. It is a good bet to supply an answer that defines a certain function that is required.
Ok, what im using is Joomla CMS. The thing, is when I try to connect to my MySQL Account, I can't, because it says "Access Denied" and I think this is because of the PHP Settings. If it isnt, then what is it?
For joomla you need atleast version 2 php, but that shouldn't stop you from getting in to the MySQL database. If you into Joomla admin panel and go site settings you can find the details to the database there.
How are you trying to connect to it?