Or in your site front page, in the admin bar find Edit Page ( Back-end Editor ) or Edit with WPBakery Page Builder ( Front-end Editor )
For changing size and margin, go to Theme Options > Header > Header > Logo element
For disabling slider or changing it with other title types
Example Breadcrumbs or Title, Go to Page Edit > Page Settings > Title Type
For overall website title type go to Theme Options > Title & Bredcrumbs
If you want to add/edit Posts, Go to Dashboard > Posts
You can edit Carousel settings in its edit settings and change the Service Box from their edit.
You can edit Carousel settings in its edit settings and change the Quote from their edit.
Instead Quick Contact also you can create any page and assign it.
In widgets find Footer 1 to Footer 4 sidebar area sections and edit them.
For changing background of Footer, Go to Theme Options > Footer > Footer Widgets > Container Style Kit
For editing menu navigation settings go to Theme Options > Header > Header > Menu Element
And for styling menus go to Theme Options > Header > Header > Menu Styles of this Row