^well you to options its either
1. contact asus and complain about their Asus download master doesnt work on your trackers.
2. void you warranty and upgrade to asus custom firmware
so if you opt to choose 2nd option, all you have to do is upgrade your router as usual like a regular asus firmware but how?
1. reset to defaults (or 30/30/30 reset) your router (refer to manual how to do it)
2. go download this firmware <click here for link>
* choose RT-N14U_126.96.36.199-081_full.trx
3. Now you can use that trx file to migrate your n14u to cfw which can be done via Firmware Upgrade page on the Asus router page or via Asus Recovery Firmware software (included on the CD).
After installation, read the this documentation regarding about the firmware.
<click here for link>