I get asked this question every year, usually more than once. While there are ways to get access to iOS 10 before the public release, keep in mind that patience is a virtue and waiting until the public release is usually the best idea.
There are three ways of legally installing:
Logins to any of your Apple accounts now use a centralized Apple ID which lets you sign in to iCloud, iMessage, FaceTime, iTunes, ADC, AppleSeed, Apple Education, Apple Jobs, etcetera. If you have this form of login, it is extremely simple to sign in to everything Apple; although the login screens do look different in different sign in areas, they all use...(more)
There are two ways of doing this, both of which are quite easy.