No need to deactivate Lightroom just remove it from the old PC. Lightrooom allows for use on two computers at the same time by one user but has no activation process.
Photoshop does need deactivating from the old PC before activating on the new.
I have LR 3.6 and now LR 4 on my old Laptop. I have LR 3.6 on my desktop. I want to keep LR on my desktop so I have to de-activate LR 4 on my old laptop. I read the instructions bur whwn I go to help Aide I can,t find de-activate. What can I do?
Montaigne, there is no deactivation for Lightroom. You can have one copies of both versions on each computer. That is Lr3.6 and Lr4 on each computer. Lightroom is unlike Photoshop which does require deactivation.
If you want to remove any instance of Lightroom just uninstall or delete the version you don't need.