Switches and routers have some firmware (similar to BIOS (UEFI) on PC). It represents a "step" before the OS (maybe I'm wrong). Can we manage this firmware just like BIOS or UEFI on a PC? On cisco catalyst 2960 switch for example. If we can, how approximately does it happen? Through a console cable or something?
Most embedded devices have a bootloader - rudimentary hardware initialization (CPU, RAM, flash) - and a more fully fledged firmware that contains the hardware drivers and the OS for normal operation.
On some devices you can access the bootloader (ROMMON on some Cisco devices) via serial console , e.g. to reset passwords, clear settings, or to recover the actual firmware after a failed update. Some devices even allow access to the bootloader over the network. On other devices you can do no such a thing. In any case, operation is usually limited to device recovery and there isn't much interesting stuff.