Was it the Android OS software that you updated, or an apps software? If it was an app, then you can try loading in "Safe Mode" and see if that will get you in, so you can remove that app or it's update.
To get into "Safe Mode" please do the following.
1. First turn off the tablet.
2. Next press and hold "Power" until you see the manufacturers logo on the screen, then release the power button.
3. "Quickly" press "Volume Down" and hold it for few seconds until you see the message "Safe mode: ON" or something similar.
4. If you wanted disable it, simply repeat the steps above, and you should see "Safe Mode: OFF" rather than on.
If it wasn't the app, and was an Android OS update (firmware), then you may need to do a "Hard Reset" to...