Remove top bar for mobile site?

Hello
How is it possible to hide top bar menu for mobile sites? When I open the site on iphone it takes to much space for top bar manu, plus i have set a separate menu for mobile sites and in this case in iphones I am having both – top bar menu and mobile menu, this is confusing and not right.

Any ideas?

By the way, is there anyway to make bigger the font size of top bar menu and spread it on whole line, do not make it stay on right or left side?

Thanks in advance.