I have a Cisco 1800 router at work. I have its IP, username and password.
How can I access it using the command prompt in Windows?
If you want to use Windows own command line you can use either
Telnet can be installed as a Windows Tool through Windows own Software Management Tool. I'd only recommend the usage of telnet as far as the network is sufficiently secure and you trust everybody on the network. Telnet does not use encryption in any way, everything that is send and recieved can be read by a third party.
There are several SSH Clients, I'd recommend using OpenSSH through Cygwin, but Cygwin is a powerful suite which might be too heavy for your usage. There are no native Clients for Windows, but several other third party implementations I have never used.
you would need to use ssh or telnet depending on how the router is set up.
Would be a good software to use