The upgrade will make all the settings back to factory and requires to reconfigure the router. The best way to avoid this is to do the settings backup before you upgrade. You can go to System tools-->Backup setting-->Save it into your computer. After you upgrade successful, you can restore the setting you saved.

The same happend to me after the latest Firmware upgrade, and the security saved BIN file from the old firmware could NOT be used, the router did not accept the BIN file, and i had to reprogram the whole router, and then make a new security BIN file, sorry but that is the only way to do it.

Typically, firmware upgrades default to "out of the box" default settings. This is what I've seen in manufacturer's firmware updates, and alternative firmware updates such as dd-wrt and easytomato.

In general, configuration settings are not interchangeable between firmware versions. Unless the company builds in logic to save the old and re-populate it upon upgrading to the new firmware version - which is a little challenging to do as you are basically wiping out memory as part of the firmware upgrade...