You can check your account in app to see if you are eligible for an upgrade. You can do this by clicking on the Check for Upgrade button under the 'My Dashboard' section.
If you are eligible you may see options for 'find a store' or 'online shop' to allow you to proceed with purchasing your new phone.
Store finder is also available on the main menu.
When choosing Online Shop you will be directed to your mobile browser, and you will be asked to login again in order to get the upgrade price that's relevant to you.