Logo/Banner Size

Hello I'm using catch responsive theme on my homepage jonashegnauer.ch The problem I have is with the logo/banner. The theme says ideal size is 150x150. Ridiculous because it is squeezing every size of image into the same banner size. If I knew this size, I could upload it already in the right size. Which is the banner size? The other problem I have is with the search field. How can I remove this one permanently(that with an update of the theme it would not appear again)? Thanks for answering! Jonas