Cool.You can get Windows 10 free without worrying about the upgrade.
Just install build 10130 and you'll get to keep it as you're classed as a "tester".
http://www.theverge.com/2015/6/20/8818383/microsoft-windows-10-free-for-testers
Just remember, Microsoft has gone back on there word before and are constantly flip flopping on the subject. They've even flip flopped on there recent announcement so don't complain if you don't get it (if You have a valid Win 7/8 License you'll be fine either way)You can get Windows 10 free without worrying about the upgrade.
Just install build 10130 and you'll get to keep it as you're classed as a "tester".
http://www.theverge.com/2015/6/20/8818383/microsoft-windows-10-free-for-testers