I am stuck in free trial on Lightroom, I have a serial number and activation code, but cannot find where to enter those

I bought Lightroom 5 from best buy, I did all of the downloads and it is on my computer, but it is in free trial mode, and I want to put in my serial # so I can use it not in the free trial mode. I have the serial number and the activation code, but I cannot find where to enter that info.