I have installed olegs 1.9.2.7-7f-pre7 firmware on my router.

I now want to install the firmware asus supplied. I have download the file "WL500gp_1.9.6.9_TW.trx" from their site. But when I select the file in firmware upgrade and select upgrade. The router write it will take about 80 seconds..... Then after about 1 minute, the screen reloads as it should. But nothing has happend, the firmware is still "olegs 1.9.2.7-7f-pre7"?

How can I roll back to the asus firmware?