The two most common reasons why you would like to reset your router are a forgotten default password or when you can't access to your router settings. A hardware reset of your router will make it like a new router with all the default settings which were assigned in the factory. All the changes you have made in the meantime will be erased.
Most routers can be reset using the reset button at the back of the router. The following steps are general steps which can be used for most routers. However we encourage you to visit your manufacturer's website for more detailed instructions which may be a bit different according to the brand and model.
To do this process successfully you will have to use a paperclip or some other pointy object.
If you can't login and you have entered the right login details, it usually means that the resetting was not successful. Therefore you will have to perform some additional steps.