How to Install Windows 10 Technical Preview?

Get Started with the Windows Insider Program

Go to Settings > Update & Security > Windows Insider Program on your Windows 10 device.
Select the Get Started button.
Follow the directions on your screen to choose the experience and channel youd like to get Insider Preview builds through.

How do you Install a Preview Build of Windows 10 OS Build 20262 or Higher?

Download Windows 10 build 20262
The preview is available immediately through the Dev Channel, and it will install automatically, but you can always force it from Settings > Update & security > Windows Update, and clicking the Check for updates button.

How do I Upgrade to Windows 10 from Technical Preview?

To get started, open Settings and click Update and Recovery. Under Update and Recovery, click Recovery option. On the right side , you will have the option “Go back to a previous version of Windows”.