picture header

My default wordpress page had a default picture as the header. Is there a way to remove it, as I just want my logo there.

I tried to upload my logo in place of the header picture, but when it appears on my site, it is slightly stretched and so loses quality (even though it looks fine when uploaded to the dashboard).

I just want my logo nice and sharp at the top of my wordpress site.

To see what I am talking about, compare:

runyourownrestaurant.com
and
runyourownrestaurant.com/wordpress

I already made the logo bigger to fill the header but it still stretches it for some reason. Weird.

Any help would be awesome, thank you.