You should go to Admin Panel -> General Admin -> Configuration and fill in the Site description field with the proper HTML code.

Code:

<img src = URL_of_the_image>

You will possibly need to change the style template, since not all allow the site description to be viewed.

Please, in future, use proper English when posting. It would make it easier for people to understand your question and you will recieve a faster reply.

SORRY
i tried but not working

Try with another style template.
SubSilver, for example.

yah working
but that thing working only at subsilver theme
or no other theme its working
why?

It is not only the SubSilver. There are others. You should chose a template in which you can actually see the site description, because the banner is put there. If you want to use any template you should pay for the removal of the ads and place the banner in the header section.