Have you done anything yet in regards to the upgrade? Does the old PC still exist as such? Can you link the licence to a Microsoft account now? If not, do you have the licence key?
If you don't have licence key, you likely need to buy win 10 licence again. If you have key, you can perhaps contact MIcrosoft after fact and explain you swapped CPU/Motherbaord.
https://support.microsoft.com/en-us/help/20530/windows-10-reactivating-after-hardware-change
As for the actual install, its really easy to wipe an ssd and put windows back on it again. The ssd isn't one use only. No need to buy a new ones.
depending on intentions, this is how to wipe any hdd with windows on it
Boot from installer
On screen after language choice, pick repair pc, not install
Pick troubleshoot
Pick advanced
Pick Command Prompt
Type
diskpart and press enter
Type
list disk and press enter
This will show the list of drives currently attached to PC, make note of the drive number of the drive you want to wipe
If Disk 1 is the drive you want to clear, type
select 1) and press enter. A message will confirm it is selected
Warning: Diskpart Erase/Clean will permanently erase/destroy all data on the selected drive. Please be certain that you are erasing the correct disk.
Once you sure its right disk, type
Clean and press enter
The Command Prompt window will display the message "DiskPart succeeded in cleaning the disk". Close out of the Command Prompt window by clicking the red X in the upper right hand corner.