Depends on what interface the SSD has.

You can clone the Dell 1tb ssd boot drive to your own 2tb ssd.  After clone the 2tb ssd will be wiped and have the 1st 1tb look exactly like the dell ssd. The 2nd 1tb of the ssd will be unallocated but you can create a new single volume on it to make a logical D: drive of 1tb. Note your ssd can be either M.2 or sata, doesn’t matter.

I would not swap an Nvme for a SATA SSD...

I have an Aurora ACT1250 on order that has a 1Tb boot SSD and a 4Tb SSD for storage.  It will be running Windows 11 Pro.  I have a 2Tb SSD laying around and was wondering how hard it would be swapping out the boot drive and to load Windows onto the 2Tb SSD?  Any ideas would be greatly appreciated…..Thanks in advance for any help.

Sounds like a nice config already. The pre-installed 1-tb SSD (likely NVMe, likely very fast and nicely matched to rest of system) ... I would just keep that. It will hold ALL Windows-11, Apps, and Programs. With about 400gb left-over for your favorite large games... and with plenty of spare working space.

Use the 4tb for Media Files or more large Games 
 
Install the 2tb SSD as E-Drive and use it for Media Files, more large Games, or backups.

Get the machine and use it for a while before you start tearing it apart. Add your spare drives, but maybe keep it mostly stock until your warranty runs out.