Reflash Tablet

If you have a build you want to install (which is made up of multiple files):

Put all its files in the root directory of a microSD card, insert said mircoSD card, and simply turn the Tablet on.
After it is done reflashing remove the SD card.

If you want to just hard reset a tablet and reinstall the same base set of apps it originally came with:

Turn the Tablet off.
Power it on holding down the power button and Volume - (minus).
You will should see an Android robot/gear screen and not get to the flashing XO character step. Like many other Android devices, use the volume buttons to go to "wipe data/factory reset" and use the power button to select. Find the randomly placed yes and select that.
Reboot the tablet.
Go through the Google customization wizard, not bothering to attach it to an account, etc.
The Tablet installer will run and install the apps + XO Learning environment/locker/etc.
At the end if it doesn't reboot the tablet (earlier OS versions), manually reboot the tablet, or power it off if ready for use (or instructed?).