I am sorry for the inconvenience caused to you.
In order to install Lightroom 6, you need to have a 64 bit operating system. I would suggest you to upgrade the operating system.
Click the link to check the system requirements for Lightroom : System requirements for Adobe Lightroom for Mac and Windows OS
Lightroom 5 does work with 32 bit operating system.
Click the link above to check the system requirements for Lightroom 5.
The serial number for Lightroom 6 cannot be used with Lightroom 5.
From where you have purchased Lightroom 6?
Thanks for your reply. I have bought via bol.com. my package is already open so I don't think I can return it.
I guess if nothing can be done, I should just keep till I have a new laptop.
You may contact them and check for the exchange if possible.
However, you will be able to use the product once system requirements meets for Lightroom.