I can not find my serial number for my lightroom 5 i downloaded and i need it for some reason when i did the latest update now its asking for my serial number
May I suggest that you develop a method of storing your ALL of your serial numbers (and other important data) so that you can find them when you need them? After all, you paid money for this.
By the way, if you downloaded the Creative Cloud version of Lightroom, that's the wrong version and could cause this problem. You want the standalone version of Lightroom: http://www.adobe.com/downloads/updates.html
I usually always do, but since this was bought via creative cloud It did not give me a serial number, which would explain why I do not have it in my records. this was just fixed by tech support, it was not my fault on my need THANKS !