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
And for changing margins go to Theme Options > Header > To of Header > Social Element
For disabling slider or changing it with other title type
Example Breadcrumbs or Title, Go to Page Edit > Page Settings > Title Type
For overall website page title type go to Theme Options > Title & Bredcrumbs
For changing this row background go to Theme Options > Footer > Footer Widgets and find Container style kit.
Instead Quick Contact also you can create any page and assign it.
You can edit row under tab General find Parallax image and replace, add or remove it.
For changing Background color, hover over content box and edit it to find Overall style kit.
For editing more contact form and mailing settings, Go to Dashboard > Contact Form 7
PS. This content box have -130px margin top, edit content box and find Overall style kit you can change margin top value.
For changing background color or border of content box, edit content box and find Overall 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