Hello Paula. You can create an image of your current operating system with something like Macrium Reflect Free edition. You can get that here.
Macrium Reflect Free
Then you can go ahead and do an in place upgrade to Windows 10 so that you at least get the free upgrade - and after the upgrade is done and activated you can create a DVD from this link here.
Link Removed
This way you have that free upgrade accomplished, and you can then simply go back to the image you have created with Macrium Reflect (or you can use Acronis) to the state your current operating system is in now and you will be ready when you do upgrade your Parallels to be fully compatible with windows 10. Hope that helps you out.