Removing classic

To remove classic first make sure the Classic Environment is not open or running. Then locate your classic system folder named "System Folder" (usually inside your Hard Drive) and drag it to the Trash and delete it. That's it, no more classic.

To re-install it you whould probably need the discs that came with your Mac. If you have multiple discs it is usually on disc 2 if I remember correctly. There should be some type of installer named "Classic Environment" or somethign along those lines, just double-click on it and follow-through the installer to get a fresh copy of the Mac OS 9 folder on your computer. Good luck!