To safely update your (often provided by Three UK or other ISPs), use the official methods:
Do not attempt an update without knowing your starting point. zyxel nr5103e firmware update 39link39
If you purchased your router through a provider (ISP), the firmware is often proprietary. In these cases: To safely update your (often provided by Three
Based on your search query, here is the information regarding the firmware update, specifically addressing the "link" aspect often associated with this device's recent updates (particularly the "39" version you mentioned). zyxel nr5103e firmware update 39link39
: Mentioned by some users as a newer version required for optimal performance with gaming consoles. Provider-Specific (ISP) : Many