For changing Logo go to Theme Options > Header > Logo

For changing size and margin, go to Theme Options > Header > Top of Header >  Logo Element

For editing mobile and tablet header go to Theme Options > Header > Mobile, Tablet Header
For adding, removing and styling social icons go to Theme Options > Header > Header > Social Icons


And for changing margins go to Theme Options > Header > Top of Header > Social Element

For editing or removing Back to Top or Quick Contact items go to Theme Options > Footer > More

Instead Quick Contact also you can create any page and assign it.

For changing Copyright text go to Theme Options > Footer > Bottom of Footer > Icon and Text Element
This items are Works post type, You can find them from Dashboard > Works

Also edit this element to see post type and styling settings.

For editing menus items go to Appearance > Menus

For editing menu navigation settings go to Theme Options > Header > Top of Header > Menu Element

And for styling menus go to Theme Options > Header > Top of Header > Menu Styles of this Row