If you're still using Windows 7, you should start thinking about whether you want to upgrade your PC, build a new PC, or buy a ready-to-go prebuilt system for Windows 10. Windows 7 will stop receiving security updates during January 2020.
The Guardian: Will I be forced to upgrade Windows 7 to Windows 10?
There is no "upgrade" pricing currently available for Windows 10, even if you're not planning a clean install. Some people might just find it cheaper to use Linux instead of Windows 10, but using Windows 10 will probably be easier for most.
If your system has at least 2GB of RAM right now and at least 64GB of free storage space, check out the minimum system specs for Windows 10 to start deciding if you want to upgrade your current system, if necessary.
Microsoft's specs recommend a minimum of 20GB for an install, but the default updating for Windows 10 is really going to go a lot better if you look towards a 64GB system at a minimum. (I'd avoid a 32GB system with Windows 10, from personal experience. It's a struggle to update.)
More coming soon!