You need to go through the Password Recovery Procedure. Here are the links, depending on how your 6509 is configured.
If you are running strictly Layer2, or if you are using "Hybrid Mode" (CatOS commands for Layer 2, and Cisco IOS commands for Layer 3 when you have the MSFC on your Supervisor module), follow the link for CatOS.
If you are running in "Native Mode" (Cisco IOS commands for everything), follow the link for Integrated IOS.
CatOS:
http://www.cisco.com/warp/public/474/pswdrec_6000.html
Integrated IOS:
http://www.cisco.com/warp/public/474/pswdrec_6000IOS.html
Hope this helps.