Hi John,
Unlike Thomson, I am not from Laminar Research; just a flight simmer from down under.
On the basis your are not running the 3rd party hybrid version of X-Plane under the Steam banner then you do not have to reinstall X-Plane and then reconfigure the software for your needs. As a sideline I do not support the steam version.
The true/ official version of x-plane should be either on your desktop, dedicated drive or an independent directory. If so then all x-plane files should be together under the X-Plane directory.
Find the XP directory and right click your mouse cursor on the root directory name and then properties to determine the directory size. You then copy the whole directory to a portable drive or an adequate capacity memory stick. Then copy from the portable storage onto your new computer in the location of your choice.
You will have to create a new desktop icon to start X-Plane.
It all should work without having to do a fresh installation and reconfigure your system. This is one of the benefits of X-Plane compared to other flight sim packages that mix files all over the place.
You can leave X-Plane on your old computer provided, as Thomson has stated, you do not run both versions at the same time.
Good luck with your new machine
Glenn