The default firmware that comes pre-installed in a lot of new routers can be insecure and problematic. For instance, a lot of new routers use something called "WPS" (Wi-Fi Protected Setup) which is enabled by default and is supposed to allow users to easily secure their network. Unfortunately, this is flawed and can give a remote attacker access to the network. In some cases, it's not even possible to disable this insecure feature.
One way to better secure your router and improve its overall performance is to install alternative firmware, if your router is supported by it. Here are two free, open source options:
It's important to note that there are potential risks associated with doing this. If the installation of the firmware is interrupted, it could brick the router, making it unusable. It's also not advised to install other firmware if your router was provided by your internet service provider. Not all routers are supported by DD-WRT and Tomato, so make sure to check before attempting the install.
To find out more about the benefits of installing alternative router firmware, check out this question from episode 1057 of The Tech Guy show.