Before upgrading to System 7, back up your hard disk using any of backup and
restore products available for the Macintosh. At a minimum, back up your
System folder.
Please do not try to install System 6 over System 7. Instead, follow these
steps:
1) To remove System 7 from your hard disk, boot from a System 6 "System
Tools" floppy disk and drag the System 7 "System Folder" from your hard
disk into the Trash can.
2) Restore your System 6 "System Folder" from a backup, or install from the
System 6 "System Tools" floppy disk.