Back Up Important Data
Save files to Google Drive or an external USB (Powerwash erases all local data).
Sign Out of Your Account
Click the time in the bottom-right corner of the screen. In the menu that appears, click → Sign out (or Log out).
Initiate Power Wash
Press Ctrl + Alt + Shift + R simultaneously.
Select Restart in the pop-up window.
Confirm Reset
After reboot, choose Powerwash → Continue.
If the keyboard shortcut fails: Go to Settings → Advanced → Reset settings → Powerwash. Here's a short video on how to powerwash a Chromebook: How To Powerwash A Chromebook (Factory Reset) - YouTube (00:00:00 Intro; 00:01:13 Back Up Everything; 00:01:51 Powerwashing)