You need to add your own custom css rules to override this. As for the date format, this is configurable in the integration settings at the back end of Komento

I've already made. the format is still wrong!

My format is: D, d M Y

The Class is <span class="kmt-author-time">Dienstag, Mai 13, 2014</span>

correct is: <span class="kmt-author-time">Dienstag, 13. Mai 2014</span>

hey torsten,
for this particuar class the settings don't apply. but you can modify this in the file components/com_komento/themes/kuro/comment/form/author.php

have a look around line 22:

<?php echo Komento::getDate()->toFormat('%A, %B %d, %Y') ?>

and replace the current one with your needed time format.

hope that helps and have a nice day