You CAN use the Oleg WL500gp upgrade firmware page. BUT heres what I had to do.
Download the firmware.
On the WL500GP
Press reset for 5 secs.
Unplug cables apart from modem.
Unplug WL500GP power wait 5 secs and plug it in again.
You should see 'DEFAULT' as a wireless network
Connect to DEFAULT
Goto 192.168.1.1 and login, you will notice all settings are wiped - get the firmware upgrade page.
Upload the firmware.
It will say 'FIRMWARE UPGRADING!' you sould not get any diconnected errors.
It will take a few mins to upload - leave it.
You will eventually get the screen of your new firmware. Mine looked just like the old OLEG version - it was a shock when i noticed so many more options.
Im my opinion the rtn firmware for the WL500gp is a major upgrade, and worth installing.