In case you are not facing any problems with DSL connectivity, i recommend NOT to change the firmware. I have multiple dsl modems. So, i could experiment on the Aztech one
In case you are ready to step ahead, open
and download router upgrade checker and run it. Keep wireless AP on while you do so.
password=the admin level username you use to open your router's web configuration
It depends on the model you have. If you have wireless router only, TP-Link factory fitted firmware is sufficient. In case you have a dsl router PLUS wireless router device, you may consider changing the firmware.
NetGear and LinkSys devices are known to work with a variety of open source firmwares. Choices are limited when it comes to other brands.
Some people have tried x-wrt on WAG160N. IMO, x-wrt or dd-wrt can work on WAG120N as well. However, you should wait till knowledge-base of any of the aforementioned firmwares states (tested) support for the model you own.
I do not know if wimax CPE by motorolla is linux based. Can you establish a telnet session with the device? I shall check a wi-tribe cpe and let you know. At the moment, there is no known open source firmware for wimax CPEs.