As Goal admin you can make other people admin or remove them from the Goal in the 'Members' area of the Goal
1. Go to the Goal you want to edit access to
2. click the three dots (show more) icon
3. Select 'Members
4. Click the pencil icon (edit button) to make changes:
You can remove users form the Goal entirely by clicking the cross next to their profile picture
You Can manage admins by selecting/de-selecting them in the pop up