Hola
Puedes seguir el siguiente procedimiento:
Upgrade process:
Copy IOS from TFTP/USB to bootflash
#copy tftp:xxx.bin bootflash:
Verify Copied file
#verify bootflash:xxx.bin
Give boot statement command on config mode
#boot system flash bootflash:xxx.bin -----------(newer)
#boot system flash bootflash:xxx.bin -----------(older as backup, its optional)
Verify the boot statement whether correct version is present or not
#show run | in boot
Save running config and reload
#copy run start or write
#Reload
Verifica el Release Notes de la version 17.3.X para mas información:
https://www.cisco.com/c/en/us/td/docs/routers/access/1100/release/17-3/isr1k-rel-notes-xe-17-3-x.html
Espero te ayude
saludos
Leonardo