I want to change the domain name for my sites. How can I do that?

I have created a community but not able to manage the login settings. It is because my profile is System Administrator and I added Community login user profile to the community member list. I didn’t know that I will not be able to edit with my profile. Is there any way I can add System Administrator profile to the member list again? I am trying to create another user with community login user profile who can edit the community but that profile is not available when I am creating the user. How can I fix the problem without creating another community?

I have created a community but not able to manage the login settings. It is because my profile is System Administrator and I added Community login user profile to the community member list. I didn’t know that I will not be able to edit with my profile. Is there any way I can add System Administrator profile to the member list again? I am trying to create another user with community login user profile who can edit the community but that profile is not available when I am creating the user. How can I fix the problem without creating another community?