How to enter U-Boot Mode？
When you press RESET button for Disconnect the power, Then turn on the power, after 15 seconds release the power.
Launch a web browser, such as IE Web browser;
In the address bar, input 192.168.1.1 and press Enter.
Select the DD-WRT firmware.
Starting the firmware update, please wait a moment.
Please upgrade your device by cable connection.
Do not power off the device when upgrading.