Use Assets : Previewing Assets : Preview Comparison : Starting the Comparison
   
Starting the Comparison
The preview comparison can be started either from the collection window, or from the fullscreen preview.
 
1. In the collection window, select the records of the two assets you want to compare, then select Asset > Compare Previews.
OR
In a Fullscreen Preview of multiple assets, select the previews of the two assets you want to compare, then open the context menu (with the right mouse button / Control key + mouse) and select ­Compare.