Which router model we have to use for configuring a cisco router as a tftp server
How to configure a cisco router as tftp server
How to backup current-configurations to tftp server
You can set up a TFTP server on any current Windows machine. All you need to do is download and install some TFTP software, there are plenty of good free ones available online. Once you've set up the TFTP server with a directory and have checked that it is binding to the LAN IP address on the Windows machine, you're ready to upload/download.
As long as there are no firewalls blocking the traffic and routing is in place between the Cisco device and the server, you can use the command that Leo previously posted on the Cisco device (The TFTP IP address will be the LAN address of the Windows machine), and your config will be backed up to the directory on the TFTP server.