Find the OS 9 system folder and drag it to the trash. Make sure that the one you trash is not the OS X one. The OS X system folder is called System while the OS 9 one is called System Folder. It may, or may not, have a happy Mac face on it.
Take the Applications (OS 9) folder and drag it to the trash. You may find other applications laying around, the OS 9 documents folder may also be trashed.

Empty the trash and you are about done.

P