Header

How can I make the header section bigger to accomidate the preset sized header image? As it is now medium size is 300×140 and it extends into the page so Id like to make the top white margin a little bigger if I could and maybe change the header color from white

Also is there some where I can set the menu button color? I just have plain white that highlight black on hover

Oh also I dont have a slider. How can I get that installed