What are the CPU options for your PC? You should start from there.
Go to Dell' support site, enter your PC service tag number, and look for the service documentation. It will tell you what motherboard is there.
Anyway - check TDP ratings of the original CPU, and the one you're trying to put in. If they are vastly different, check cooling solution on your computer - you might not be able to upgrade it.
You can also check release notes for BIOS upgrades, they usually list supported CPUs.