V9 can be installed on three (3) devices but you may only run it on one (1) device concurrently.
See the End User License Agreement (EULA) for more details.

To change from one computer to another, simply use the same login information used during registration.
See the Quick Start Guide (Installation - Register your account) for more details on how to register.

Note: The WiFi Device can only be setup on one PC at the same time (See also FAQ 100635)