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
This element has -70px margin from bottom that you can find it in Button Styling stylkit of this element.
For example you can change styling of content box such as border, background, colors, Box Shadow, etc.
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
This element has -35% margin from right that you can modify it in Container stylekit.
This element has -200px margin from top that you can modify it in Container stylekit.
This element has Background Layer, you can find it and edit too
These service boxes have border from bottom or right that you can find it in Box Container stylekit
This custom class has been set in Theme Options > General > Custom Codes
This row also has -330px margin from top that you can find it in Row Settings > Design Options
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
This is Offcanvas Widget element in header, for editing content of widgets go to Appearance > Widgets > Offcanvas Widget