Greeko85 :
I'd be looking to replace it if I were you. Looks to be basic at best- I'd consider a cryorig h7 or 212 evo if it fits in your case
Using non Dell CPU heatsink is not that simple, you can not just buy one and attach it - Dell motherboard has custom back plate, which has to be removed, without damaging motherboard.
So, first, we have to troubleshoot your existing situation.
Arctic Silver 5 instructions for your 1st generation of CPU (you have, most likely anything from i7-920 to i7-970, all 130watt).
http://www.arcticsilver.com/pdf/appmeth/int/vl/intel_app_method_vertical_line_v1.1.pdf Basically, vertical line application.
Next, is the CPU fan is spinning? Is CPU heatsink is clean from dust?
If everything is working as it should, but temps are still high, then we proceed to new CPU cooler installation.
By the way, where do you live geographically. Summer idle temps can be very high, so if you can not breath in your place due to high temps, PC would not be able to function as well.
I am in Southern California. I had to shut down my PC a few times past summer due to high temps and I have Noctua 120mm dual fan cooler, which is the beast comparing to yours.