New Computer, Install Photoshop CS6

Hi everyone,

I recently got a new laptop (windows based). My old laptop (also windows based) was my late father-in-laws. That laptop had Photoshop CS6, and I would like to transfer it to my new laptop. I have tried registering the product under my account and entering in the serial number, but it tells me "The serial number provided has an invalid format". How can I get Photoshop CS6 on my new laptop?

Thank you!!