first plug an ethernet cable to pc and the tp-link mr3020. we use cable because it's more reliable than wireless. because upgrade firmware need stability. make sure pc power keep on while doing these action. because if the main process got interupted while updating firmware, it can brick the hardware it self. so using an ups is recommended.
change the ip of your lan. in windows 7 it can be done from start > control panel > network and internet > network and sharing center > adapter setting > local area network > properties > tcp ip v4 and change the ip from 192.168.1.1-X (X= any number from 1-253)
the default user is admin and password admin
on left side bar u can find system tool > firmware upgrade. choose the firmware that we already download.
when asked are you sure bla bla bla... just press ok.. then wait until the router reboot. after that check the status bar.
voila... the router just upgraded well. you can see the version changed after we flash the new firmware. that's it