As of this morning, April 3, the Ancestry.com website for the 1940 census is still uploading the images, so most states are not yet available on this site (including Utah).
The National Archives website does have the images, if you are willing to search. Check out the National Archives site to search by enumeration district. If you know where your relatives lived in 1940, you can use the enumeration district maps provided on the site to locate the district number, and then browse the census until your family is located. Great instructions are provided on the website to make searching easy. Happy hunting.