I have a two-year-old WD Black HDD in my old Windows 7 desktop.  I just bought a new Dell XPS running Windows 10 with a 1TB HDD and a smaller SDD.  What do I need to do to the old WD Black drive in order to install it in my new machine?To be honest. it is not worthwhile.
The old drive ILL not help new PC. 
I think now dell XPS is only a model of dell laptop, If it is then the desktop drive will not fit or there will be no slot FREE. You could use it in a caddy. Or perhaps use a NAS box.

Caddy
 
 Dell offers both XPS desktops and laptops.

Provided your XPS is a tower desktop model then the odds are pretty good that it can accommodate the 2TB drive.  You will need to see if there is an open SATA port on the motherboard of the computer.  If there is then you'll need a SATA cable to connect from the motherboard SATA port to the data connection on the drive.  You will also need an available power connection from the power supply.  Once you have both of those, then you need to physically install the drive in an available bay of the tower.

Once the drive is physically INSTALLED and electrically connected to the system, the drive should then be able to be accessed from Windows EXPLORER when the system is booted.  If the drive was a boot drive in the old system (meaning it had the Operating System on it) then you should format it to rid it of the old OS and to free that space.  If there is data on the drive you wish to keep, back that data up before formatting it. Keep in mind it will not boot to Windows on the new PC...hook it up tp SATA port 3 or higher to prevent it trying to.