to change a ight switch?

You don't mention the colours or how many wires.

If you have two wires at the switch (the usual arrangement) the Red one goes in Com and the Black one can go in either of L1 or L2 it does not really matter. If you wish the switch to work "the other way up" you can either turn it upside down or move the black wire to the other L1, L2 position.

The new switch has the ability to connect Common to either L1 or L2.

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If you have three wires at the switch positions (two switches controlling one light) connect the red wires to Com and the other wires to L1 and L2 any way round.

Like this...
http://www.electronics-project-design.com/images/TwoWayLightSwitch.GIF

Good luck.. Take care...

Peccavi
April 2009