How to Zap the PRAM on A Mc Plus Running System 6

>You zap the PRAM on a System 6.0.x machine (and earlier) by doing
>one of two things:
>
>1.   If you are running a Mac Plus, 512KE, 512 or original 128, the
>      only way of erasing the PRAM is to remove the battery that
>      maintains said data. The battery is found behind a relatively
>      easy to open door on the back of the machine.
>
>      You have to keep the battery removed for about an hour to
>      guarantee the PRAM contents are lost, because a capacitor on
>      the logic board which actually maintains power to the PRAM of
>      these early machines takes at least a little while to drain
>      free of charge.
>
>2.   If you are running any other machine capable of running System
>      6 (eg a Mac II-series box, an SE or SE/30 or the Portable,
>      PowerBook 100 or Classic), you zap the PRAM by holding down the
>      Command, Shift and Option keys while choosing Control Panel from
>      the Apple menu.
>
>      You will be presented with an alert box asking if you really
>      want to Zap the PRAM. Click the Yes button to do the zapping.
>      [close the control panel and restart to complete the operation]

Apple Tech Info Library Article - very informative