Hi Friend,
It is always recommended to take the backup of your configuration first because sometimes after upgrade supervisor looses the configuration.
Also if your sup have enough space available on bootflash do not delete the old image and then upgrade the new image so that incase while upgrade if image goes corrupt or some porblem in image there is still old image to recover your supervisor.
If the sup bootflash does not have enough space and you have pcmcia card you can take the backup of your old image on your flash card and then upgrade new image OR vice versa you can put new image on flash card and boot the sup from flash card also.
Also after upgrade before reloading the switch make sure you double check your boot path and configuration register value to make sure everything is fine and then your last step reload the switch.
Also I am providing the link for upgrading images on cat6500
http://www.cisco.com/warp/customer/473/161.html#maintask2
HTH
Ankur
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