ROUND LOGO ON TOP OF NAV

Good morning
Please I will like to say that your theme has passed virtaually all the requiremenst that we seek in a theme.
There is just one problem we have

We have a logo that is round and when place on the site, It is really small as it is a hight of 100 px

We decided to increase the size to 150 but it still displays small

Please is there a way to do it so that the logo is the exact size without fitting directly into the navigation box. like as if its hangin

Like http://www.bk.com/

where the logo comes out of the navigation bar.

Thank you