Is your trial version possibly the Creative Cloud version?
Where did you purchase your copy of Lightroom?
Did you purchase a student or academic version?
Did you purchase an upgrade version?
What OS are you using?
•Yes my trial version is creative cloud version
• I got light room version 5.0 as free gift with one of it product I purchased
• I am using window 8 operating system
Sent from my iPhone
The creative cloud version and the standalone version are governed by completely separate licensing parameters. It will be necessary for you to uninstall the creative cloud version. Then you will be able to install the standalone version and use the serial number that you have. Uninstalling the program will not remove your catalog or do anything to the work that you have already done, and you will be able to continue after installing your standalone version. Take note however, that if you installed from the disk you will be installing Lightroom 5.0, and will want to update to version 5.6 immediately.