The cpu is removable, not soldered on. If you can get the custom dell heatsink off, then an upgrade is possible. But it's hit or miss. Dell offers no tech support that I know of for cpu upgrades; it may work or not. Best to post your question in the dell forums with your system id or motherboard model for better suggestions.
YOu will need
Coffee filters to clean CPU (dont leave lint)
Isopropyl alcohol 90% available at pharmacies cheap
Thermal Paste - Most common is Artic Silver 5-not the best anymore
but it stills does a decent job and is easy to find at elecrtonics and office stores
there are better pastes available online
just search on Toms for "thermal paste" and read the newer articles
this is a link to applying thermal paste from Artic Silver
it is the same application for all brands
link - http://www.arcticsilver.com/intel_application_method.ht...
this is a guide for installing LGA 775 cpus (mainly have to see how latch works and how to align processor in socket)