There isn't a 'deactivate' per-se. Did you buy the 'retail' or OEM version of Windows Pro?
If OEM: Your key is technically bound to your laptop's motherboard and will get flagged when you use it on the new PC. From there you'll need to contact Microsoft Support to get it unflagged.
If Retail: You can install the OS on a different computer without having the key flagged. As long as only one computer is currently running Windows 10 you'll be fine.
To get the current OS off your laptop the easiest thing would be:
- Backup any important data off your laptop you want to keep
- Load up the Windows 10 Installer on the Laptop
- Get to the point where you choose which drive to install on, from here choose to delete the laptop's current hard drive partition.
- After that you can format the drive again and close out the installer without moving forward and installing Windows 10 again on the laptop.
This way you've wiped the drive and your laptop won't conflict with your PC's new OS.