You shouldn't need any firmware from online to update or reset a tablet. The tablet is actually capable of getting the right Android version on its own. It sounds like you got something bad. Either the files were wrong, or they are damaged. If you have already cleared the tablet of your own personal data before (when the change was made) then I would suggest using the following to resolve this.
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...