It is worth it to at least take the upgrade to 10 to get your free key then if you hate it within 30 days (I suggest doing it in like 10) you can go to settings, update and security, and pick recovery then pick go back to 7 and it will basically load an image it creates of the windows 7 before it upgraded to 10. While in 10 run this tool to find your windows key for 10 when you get it and write it down.

Remember: After the 30 days you can no longer roll back to 7 as it will erase that image it made of 7. If you do not take the upgrade before July 29th then it will cost you at least $119 to upgrade in the future.
http://www.nirsoft.net/utils/produkey-x64.zip (free app to read your key it will generate for you)