Can't change logo in Word 2007

[jrasicmark]

I've been given a Word document where they want me to change a logo that is already there.
Normally, I would right click the graphic and select "Change Graphic", but that option is not there when I right click this image.
The image doesn't seem to be inside a header, but there is a blank, empty header at the top of the page above the logo.


The logo is on the left side of the top of the page, with a text box on the right side.
When I try to select the empty space next to the logo, it selects the inside of the text box instead. When I try to delete the logo, the text box expands to fill the top of the page and the cursor goes right back in the text box. Then when I try to insert the new logo, it goes inside that text box and the text does not flow around it like it did with the original logo that was outside the text box.
What am I doing wrong? How can I get this to work?