Editing or Removing Xenforo Footer Copyright in in Xenforo
To edit or remove the copy right line Forum software by XenForo™ ©2010-2017 XenForo Ltd.
Go to /src/ folder and open the file XF.php file with notepad ++ and click Ctrl+F then find below code
>return 'Forum software by XenForo™ ©2010-2017 XenForo Ltd.';
If you want to remove this code, you can remove above code and save it.
and you can change the line / code to add your website link.