Updating fully qualified urls

Uat.x.com many of the references to images or links on pages are fully qualified.

For example:
The page uat.x.com has an image on the page.
The url for the image is in the html as uat.x.com/.../logo.jpg

When we dry run go live we will use the domain x.com however all the fully qualified urls still reference uat.x.com

Two questions
1. Shouldn't all the URLs be relevant? Any idea where to look to see why they aren't?
2. Is there a way to 'mass update' all of the pages to change uat.x.com to x.com?