You dont need photoshop, nor do you need much skill.
 
just download DDS converter (its free)
 
Convert:
- The DDS file with the audi front lights
 - The DDS file with the dark rear lights
 
To Jpeg
 
Open Microsoft Paint, or whatever drawing program you have and:
- Load the dark lights file.
 - Using the square select tool, draw a box around the dark lights only, do not draw round the front lights or anything else
 - With the dark lights selected, press edit > copy, on the top menu bar
 - Now open up the Audi lights file.
 - Press edit > paste on the top menu bar
 - Now that the dark lights have been pasted, move them to the right place on the picture (on top of the standard rear lights)
 - Save the file
 
Finally, convert the file back to DDS
Or just get Cobra to do it for you 
