Custom firmware can unlock many features that a typical router is capable of.
The majority of low end routers lack the following functions, such as QoS, wireless bridge, advance bandwidth monitoring etc.
There are two main alternative firmwares to choose from; DD-WRT and Tomato.
In order to take advantages of the custom firmware and added features, check the compatible list to find out whether the existing router is compatible with the firmware.
Read the flashing process and proceed closely to the instruction. Failure to comply with the instruction may result an unusable router.