Editing header and main menu positions

[ Moderator note: moved to Fixing WordPress. ]

Hi all,
Sorry if this is a noob question but I hope someone will be able to help me out.
I’m using a theme called Melissa, which in turn uses Cherry 3.1.5 as a parent theme.

I have the base for a website, which is great but I would now like to move the logo to the center for the page with the menu directly below it.

Can anyone offer some advice on how I would achieve this? I am new to .php so please be gentle with me!

Kind regards
Sophie

[ No bumping please. ]