Take and share some pictures of the final effect.
I have tried the Dell upgrade cooler and it is a very easy install and works better than stock one. I recently installed a Vetroo V5 CPU cooler. It is a close fit so I cut out an opening in my side panel and put clear plexiglass on outside. This allowed more space plus to see fans with lites on. The Vetroo V5 lowered my CPU temps dramatically, 10 to 15 C lower. This fan is a must for any Dell XPS 8940. I also have installed front fan and went further by drilling holes in front panel to aid the front fan. Works great.
XPS 8940, Vetroo V5 CPU cooler