@chitra150 

There are two methods to update firmware for TP-Link Archer Router:

Online Upgrade:

    1) Using the web management interface, go to Advanced -> System Tools -> Firmware Upgrade to check for online updates.

    2) Using the Tether APP, go to Tools -> System > Firmware Upgrade to check for online updates.

Manual Upgrade:

    1) Download the firmware from our official website: https://www.tp-link.com/support/download/.

    2) Login the web management interface of the Router, go to Advanced -> System Tools -> Firmware Upgrade, upload the downloaded firmware and start the upgrade.

For more detailed instruction, you may refer to the FAQ: How to Upgrade the Firmware on the TP-Link Wi-Fi Routers

If you are still not sure, please let us know if your Archer AX1800 is EU, US or any other versions, and what the current firmware version is.

By the way, please also share with us screenshots of the error message and let us know usually when the error message appears.