What file holds software registration key?

When I install a software, I enter the right registration key and a wrong activation key. The software install took it. But after installation finished it said I have to renew the registration. I have to remove the software and redo the installation. However since it put the registration key somewhere in the computer at the first installation, I am not able to do it.

I have to delete the registration info on the computer. Can someone tell me where it is? Thanks a lot