Well an update won't change it turning on and off on it's own, nor would it help with slowness. Also, if there is nothing listed within the tablets updates (in settings) then there is no update for that device.
What you can do to speed it is up is first check it for viruses, malware, bad apps, etc. If any are found, remove them and then restart the device (turn it off and back on).
Should that not be enough, you may want to consider backing up all your personal stuff from the tablet to a google account or a computer and then "Hard Reset" the tablet. This would wipe everything on it and allow you to start fresh. So unless there is a hardware issue, it would run smoother after that.
NOTE: Doing this will clear 'all' the data on your tablet, so it is suggested you not choose this option unless you have to, or aren't worried about losing anything on the device.
Be sure you back up any data you want to keep, to a computer or cloud account, before doing the reset.
To "Hard Reset" the tablet...
1. Make sure that the tablet is actually powered off.
2. Remove your SD card, if there is one in the device.
3. Press the "Power" and the "Volume Up" buttons, together, until you see the start-up logo on the screen.
4. Once you can see the logo, release the buttons and allow the device to enter the "System Recovery Mode".
5. Next use "Volume Down" button to get to the "wipe data/factory reset" option When in recovery mode the "Volume Up" and "Volume Down" buttons are how to can navigate and highlight what option you need.
6. Once you have selected the "wipe data/factory reset", press the "Power" button to select that option.
7. On the following screen, repeatedly press the "Volume Down" button until the "Yes - delete all user data" option is what is selected.
8. Then press the "Power" button to hard reset the tablet.
9. If you took your SD card out in step 2, when the device is up and running again, reinsert the SD card.