You can update your router using the web interface or the TP-Link Tether mobile app.
The firmware for the V3.20 version must be downloaded and updated manually, unlike newer versions like V4 which support cloud-based updates. [OpenWrt Wiki] TP-Link Archer C6 v3
Verify your sticker says V3.20 ; using the wrong version can brick your device.
(EU Version): You can find the latest European firmware on the TP-Link Baltic Download Page Archer C6 V3.20
You can download the firmware for your TP-Link Archer C6 V3.20 from the official TP-Link website. Here's how:
