Hi SimoN,
Welcome to the forums. Let’s see if we can get you up and running on this as soon as possible here.
You need to go to :
Admin > Channel Administration > Channel Fields
This will then show you a list of Channel Field Groups which contain your custom fields.
This is why you’re currently only seeing the Rename & Delete buttons as those are the only available options there.
To find what I believe you are asking for though you need to click on the name of one of those groups and then you should see what you are looking for in the next screen on the top right hand side of that page.
I’ve attached a screenshot to show what it should look like.
Let me know if that helps.
Cheers,
Mark