If you upgrade to Windows 10, your accounting data should be retained, as long as you don't format your hard drive during the installation process. However, it's always a good idea to make a backup of your data before upgrading or making any changes to your system.
If you create a backup of your accounting data on a USB stick, you should be able to restore it on Windows 10. As long as your accounting program is designed to run on Windows 10, it should be able to read the data from the backup and import it into the program.
It's worth noting that while your accounting program may be designed to run on Windows 7, it's always best to use the latest version of the operating system that is compatible with your hardware and software. This is because older versions of Windows may not receive security updates or may not be compatible with newer hardware and software.