To answer #1: Preference file and other file locations | Lightroom CC and 6 although ideally you should be keeping track of all of your serial numbers, not just Lightroom, so you wouldn't even have to ask this question
To answer #2: I don't know
To answer #3: You need to sign out of your license on the first PC. This can be found under the Help menu. Then How do I move Lightroom to a new computer? | The Lightroom Queen
Which version of Lightroom have you bought?
Where do I find the licence number and How do I uninstall it on the old PC and then install it on the new one ?
To locate your serial number effectively refer Find your serial number
Simply uninstall it from old PC if using Lightroom version 6, Refer Activate and deactivate Adobe products for other perpetual versions.
Hia Akash, the problem is that I don´t see the product on my ID. So if I deactivate it then the track is lost and I presume can´ t install it on my new PC.
We will take care of your next install.
I have sent you a private message regarding your Serial number. Please check.