You cannot amend personal details on the app, you have to log on to your account on the website. I apologise if that is what you are trying to do.
That's interesting Beardy.
I am in fact using the website even though from my mobile. Diving in reveals that I cannot change a delivery address whilst a delivery is scheduled for that address.
The error is theirs because I put the post code for the delivery address in and then selected the correct house from the drop down. For some reason their crappy system took my billing address and used that except for the post code which is correct.
I expect that my delivery slot will not be honoured once they correct their error.
Not the greatest experience ever.