Yes, after registration, you have the possibility to upgrade at any time. You have to log in and choose the menu item "Upgrade Now". At the bottom of the page you can upgrade to a premium membership. You can choose between "upgrade to silver", "upgrade to gold" and "upgrade to VIP". Click on the membership that you have chosen and you'll get to a page with further information where you can decide upon duration of the contract. Confirm your choice by clicking on "Upgrade to Silver/Gold/VIP", at the bottom of the form.