Try the official Tenda download center and filter by "N301" — if v6 isn’t listed, contact Tenda support directly. Sometimes the v6 uses the same firmware as v5 or v4, but double-check first.
The latest firmware update for the Tenda N301 V6 brings several improvements and fixes to the table. According to Tenda's official release notes, the update addresses issues related to: tenda n301 v6 firmware update hot