CSS Customization Help with 3rd Party Theme

Hi Team,

I am new to WPMU DEV and not sure how to ask for Help.

I need help in customizing (Not a big change) one of the themes I am using in my website.

Right now I have a resolution slider in my homepage with top header with menu. My requirement is to have a full screen slider in my homepage with Menu on top of it.

Please let me know what other details I need to provide to assist on this regard.