This has been posted many times, but bears repeating. If you purchase a new computer with Windows 10 loaded in, it will be fine. You should not have any problems at all. But, DO NOT upload windows 10 on your existing device. You may be one of the lucky few who do not have a problem, but, are you willing to gamble on that? The company will continue to support your system for a very long time. You d o not have to worry about it. By the time they stop supporting the current systems, you will probably be in the market for a new computer anyway.
If you are a gambler and want to use their 'free' upgrade, PLEASE back up everything you have because chances are really good you will loose it and need to go back to your older system.