Launch Xojo, choose "License Keys" from the drop-down menu (Windows & Linux: Help > License Keys, Mac: Xojo > License Keys) then click "Update". Then sign in using the same username and password you use at xojo.com and on the forums. Your keys will be downloaded automatically. If this doesn't download your license to the Xojo IDE, go to your license key page at the Xojo website and verify you haven't used all your activations already. If you have free activations but see the machine you are trying to activate on now already listed, OR if you don't have any free activations, click the 'x" next to a machine to deactivate your license from that machine. This frees up an activation. Then, Sign In to the Xojo IDE on the new machine to activate your license there. Remember that both username and passwords are case sensitive. Xojo Lite licenses allow for 1 activation at a time, Xojo Desktop, Web & iOS licenses allow for 2 and Xojo Pro and Enterprise allow for 3. Visit the Xojo Documentation for more tips.