Before downgrading, consider:
Remember: – Never interrupt power, never use a wireless connection, and always verify the MD5 checksum of the firmware file if available. how to downgrade tenda firmware
Before you start, note that this process carries a risk of "bricking" (rendering unusable) your device if power is lost during the transfer. Tenda W330R - unable to downgrade firmware - DD-WRT consider: Remember: – Never interrupt power