In order to install Lightroom 6, you need 64 bit operating system.
Please click the link for system requirements of Lightroom : System requirements for Photoshop Lightroom for Mac and Windows OS
I would suggest you to upgrade your operating system.
Hope this helps.
Upgrade to a 64-bit operating system. Unfortunately, there is no other alternative. Beginning with Lightroom 6/CC Lightroom is 64-bit only. It is specified as such in the system requirements, which most people don't take time to read.
Thanks for the reply. Got a refund - much cheaper!