I have Xojo for Windows on a laptop but want to install it on a new machine. Is there a way to deactivate/reactivate the license or should I just uninstall/reinstall it?
On https://www.xojo.com/account/licenses/ is a “X” before each Machine. 
You may be able to have your licence on both computers. I am just not sure that the desktop licence allows it. Now, to move your licence:
- On the old computer, you open Xojo. Go to Help/Licences, select your licence in the listbox and then click Remove. Close Xojo.
- On the new computer, open Xojo. Go to Help/Licences and click Add. provide the required information . Your licence should now show on the new computer.