Some asked to me, some others did not. Thank you very much to users who are asking before remove. :)
I agree for everyone to HIDE the "powered by JoomlaComment..." part, NOT TO REMOVE.
Hide means to add "display:none" properties. Not to delete lines.
Just add the following line in the css of the joomlacomment template (or joomla template).
#poweredby { display:none; }
To customize (copy...) your template please refer to article 3.20: customize your own template
Thank you very much to respect !