Are you using the app or the website?
I only use the latter. To change details, you click on your name on the top right and select "Personal details" or "Signature".
I have never used the app so can't help you there.
And you are certainly not "thick" in not knowing this.
I'm on the website on my iPad - always done it on my iPad, I've tried doing that but can't find an edit button - tried tapping on it then tapping harder, then tapping harder still haha - no joy!