1.Before you upgrade write down all current settings as you need to enter them manually after upgrading. 

2.Run tftpd32.exe,and keep it being on till upgrades successfully.

3.Log in to the Router by typing http://192.168.1.1 in the address field of the Internet Explorer. Both the User Name and Password are admin unless you have changed it.

4.Click System Tools > Firmware, Click Upgrade button, Wait for the router to reboot.
Note: make the IP address of tftpd32.exe agree with your computer, and so does the name of .bin file.

 
5.Verify that the router firmware was upgraded. 

6.Reenter the settings you noted down before upgrading.