It looks like to change the headlights,,,it may be necessary to remove the front bumper,,,,
Here is a webpage that shows the procedure,,step,,by,,step.
The pictures you will see show the procedure for a cadillac cts,,,
The front of a cts model,,,looks almost like the front of a dts,,,
You can also post a question to : cadillac owners.com
Source: cadillac owners dot com