The IOS is not the same as the router's config. The IOS is the underlying operating system of the router, and includes numerous low-level software routines to keep the router functioning. This is similar to Windows on a PC. The operating system is Windows, while the Desktop with all it's icons and shortcuts is analogous to the "config".
How to Copy the IOS
NOTE: you must reboot afterwards
copy IOS from TFTP to flash: copy tftp flash
copy IOS from flash to tftp: copy flash tftp
copy IOS from flash to DRAM: boot system tftp
copy IOS from ROM to DRAM: boot system bootflash