To edit the users within your account, select Settings > System: Users.
Select the user you want to edit the permissions of.
Once in the users area you are able to change a user's permission level under the drop down box called ‘Role’ to either 'User' (permissions exclude all admin abilities) or 'Admin' (permissions include all admin abilities).
You are also able to edit user account details from here and lock users out of the system if required.
Make sure you click the ‘Update’ button to save your changes.