How do I edit an existing county

I don't knowhow to edit an existing country in hoi4

What are you trying to edit specifically? 

I am trying to take away land from the uk but not give it to a new country.

Are you giving it an existing country? So for example, lets say you wanted a United Ireland, you would create a new country, but use the IRE tag when creating it, and use the states section to take the territory from Britain. You can use the Import Menu and import the localization and country files from your default game to prefill out information and save time. Otherwise you will have to edit the state files individually.

Oh ok thank you.