external only... air in a can - just don't huff it. or start unscrewing stuff. What kind of notebook? I'll tell you how hard/complicated it is to take apart if you post up the model.
You can clean out the keyboard with air-in-a-can and then open up the memory or other bays (with simple screws) on the bottom but I don't recommend taking that model apart. On top of the standard screws they use plastic clips to snap the top & bottom halves of that laptop together and they have a tenancy to break. Plus that's new enough that I think you are still under warranty. Why do you have dust in there or what leads you to believe there is so much dust in there? The other thing you can do (and this is RISKY so only do it while under warranty) is blow the air backwards IN TO the CPU heat exhaust. This will loosen up the junk but could also clog/bind the CPU fan - so if it's under warranty Dell would send a tech or repair it for you. If not I don't recommend doing that.
"Why do you have dust in there or what leads you to believe there is so much dust in there?" The fan runs more frequently than in the past, even with CPU running around 25-30%. Is there a good way to get a read on the CPU temp? I see what you mean about user non-friendly snap together parts. http://www.insidemylaptop.com/disassemble-dell-inspiron-17r-n7110/