Are you trying to upgrade the IOS for your 7609?
If yes, you do not need to remove the Supervisor at all.
1-You just have to find the IOS version you need
2-Load it into the flash card on the both Sup modules
3-Change your boot variable to reflect the new IOS.
4-Save the config
5-Reboot the router
6-After the reboot, make sure that the Sups are in SSO/redunadant mode by issuing "sh red" command
Make sure to do all of these in an outage window, because there will be down time