NEED EMERGENCY HELP WITH FULLSCREEN THEME.

I NEED HELP MAKING THE BAR THAT CURRENTLY SAYS SWEAR TO FLY ON MY SITE SWEARTOFLY.COM TO SHOW MY HEADER IMAGE INSTEAD THAT I HAVE MADE THE EXACT SAME LENGTH.

I HAVE THE HEADER SAVED AS HEADER.JPG READY TO UPLOAD, I JUST DON’T KNOW WHERE TO DIRECT IT IN MY THEME.

THE THEME IM USING IS CALLED “FULLSCREEN”

I NEED THE HELP OF ANYONE WHO MAY KNOW ABOUT THIS, PLEASE!! IM IN DESPERATE NEED OF SOME HELP WITH THIS ONE.