Increase width of wrapper in header

Hi, at the moment the logo and menu in the header of my website is within a wrapper with what seems to be a fixed width, and if I add any more menu items the menu becomes offset below the logo. I’ve tried changing the attributes that point to the header width but nothing seems to change this.

Could someone kindly point me in the right direction to make it so the wrapper extends the whole width of the header and page and center the contents within? Thank you.