Read ALL-directions BEFORE-starting:
Place bucket underneath garage-disposal/drain.
Turn OFF garbage-disposal's-electrical-power;
Verify OFF with non-contact-voltage-detector or multi-meter/volt-meter.
Loosen & remove drain-pipe(s) with pipe-wrench(es);
you might require some-specialty-tools/wrenches
to loosen pipe-fittings to garbage-disposal/sink.
After garbage-disposal & drain-pipes are removed,
measure (& cut) new-drain-piping required for either:
no-disposal or new-garbage-disposal.