I can only change the display name
Field type cannot currently be changed (but stay tuned).
You cannot edit the field key because enabling this would involve allowing the system to change your data, which we never do. To understand this, imagine you have a collection with 100 items and a field with a key named "field1". Each item in your collection has a property with that field key name and its corresponding value. Now you want to change it to "field2" . To change the field key the system would need to go into your collection and change the property name for that field in all your items to field2. If the system didn't do that, you would have a field with the key "field2" but it would have no values because all the items in your collection would still have items with a property of "field1". Since we never touch your data, we can't change the field key.
If you don't want that type or key I suggest you just hide the field and ignore it.
I should stop reading this forum when I'm sleepy... all good now. Thanks.