The command to upgrade IOS and ROM Monitor differs.
ROM Monitor upgrade from TFTP server
Router# upgrade rom-monitor file tftp://ip_address/image_name
ROM Monitor upgrade from FLASH (if you doownload the image to FLASH from TFTP Server)
Router# upgrade rom-monitor file flash:image_name
You need to reboot the router after successful upgrade - by right, the router will reload automatically.
WARNING: Do not power off the router while the upgrade is in progress.