I am not sure that I really understand your question. But let me attempt an answer and if I am not on the mark then perhaps you can clarify what you are asking.
New versions of IOS code are maintained by Cisco. Access to the new versions is restricted to routers that are covered by an active maintenance contract (and perhaps in a few other situations such as a security vulnerability). If your router is covered by an active maintenance contract then you (or an authorized person who helps you maintain your router) can download the new code from Cisco and use it to upgrade the router.
On the router the IOS code is stored in flash. If you are authorized to update the code you would download the new code from Cisco to a PC in your network. You would then copy the new code from the PC to the router. And you then might need to update boot system commands to have the router run the new code the next time that it reboots.