Take a look at this tutorial:
http://www.concrete5.org/documentation/how-tos/editors/edit-or-remo...

Any content you put in the My_Site_Name block will show up there.

Let me know if you need any additional help.

Hi thanks for the quick reply. Your hint was realy helpful! I got an image now into the menu bar. Is there also a way to change the position of it? because at current position it is cutting off parts of the image. As you can see in attachement. Thanks in advance!

Sure, look in the theme's main.css file (theme_clearview/themes/clearview/main.css) for '#header #logo a' and change the padding property. (maybe to 0px 10px 10px). Just play around with it. You'll also probably need to clear your site's cache and/or browser cache after making the change in the main.css file.