make sure you have update.zip in nand or sd card
when is choose system update it states NOT FOUND PLEASE MAKE SURE YOU HAVE UPDATE.ZIP IN NAND OR SD CARD.
How can I fix this?
If you are trying to update your tablet, I'm not sure if you can anymore.
When you try to update the system from the Settings menu (is this what you are doing?), the message you are receiving, indicates that it is programmed to either automatically download the update from the Envizen website if one is available or that you can manually download the firmware update from the Envizen website, store it on the SD Card and run the update from the card.
The Envizen website appears not to exist anymore. According to the User Manual Envizen VM100, for customer support you should contact service @envizendigital.com. When you lookup the envizendigital.com website it doesn't exist anymore.
Do you have the file called UPDATE.ZIP ? And is it the correct file from Envizen for your tablet? I would contact them to make sure. The OS updater service is looking for the file and for some reason can't locate it. It needs to be on the system on the main flash storage (NAND) or SD Card.
You also need enough space on the NAND for it to expand. You may need to delete or copy off as much stuff as you can (i.e. pictures, games or books). Frankly I would make a full backup externally to be sure I don't loose anything.