It updates when cPanel updates it.. cPanel usually delays updates on 3rd Party software due to compatibility issues that may arise. If there is a cPanel update available that contains an updated phpmyadmin (I don't know), I'm sure it will be applied soon.
Make sure your using the "Account Username" from the "Welcome to x10Hosting" email and the password you chose during the setup. Also make sure your logging in at the "cPanel Address" specified in that email.