Once you have the file, here is how to upgrade your router.
If you need help resolving a specific error during your upgrade, please tell me: What are you seeing? What ROMmon version is your router currently running? Download C2900-universalk9-mz.spa.157-3.m8.bin -
To download the IOS image for Cisco 2900 series routers, the official and most secure method is through the Cisco Software Download portal. Official Download Procedure Access the Portal : Visit the Cisco Software Central page. Once you have the file, here is how to upgrade your router