When a manufacturer buys a custom machine with a custom application, do they own the source code

I have a friend who works in a factory. He told me that one of the machines he operates runs on Windows XP. The machine has a custom program that can be configured to set the machine to run at different speeds, different jobs etc. However, they are experiencing lots of problems with the software and lots of BSOD.

I am wondering if we can migrate the software to a Windows 10 machine, but in order to do that, I'm assuming we will need the source code to patch it and get it to work on Windows 10.

So my question is, since they bought and own the machine, does that mean they own the software? Can they edit it anyway they like?