resize logo in header

I am wanting to resize the header logo image here - http://www.northernguitars.co.uk - ideally needs to be 600px wide and 150px high - whats the best way to do this and keep it responsive for the smaller screens ?

You would need to create media queries for smaller screens or use max-width property to force image image responsiveness.

OK so if I sorted the media queries further down the line, for now what is the best way to resize the logo in the header ?

From what I see you have already followed my advice in other thread and increased logo size.