Did you go into that then click next? What happens next?
If you're on the iUP and want to upgrade you need to go straight to the link to check eligibility (this is in the Apple Store app, BTW, not the website). If you're eligible it then asks you to choose device, spec and colour, then you can choose the store to reserve at and a time slot. It then confirms everything and offers to add it to your calendar so you don't forget (as if!). You don't need to give any details other than name, email address and mobile number.