Newbie Light swtich help

[forest150]

Hi,

Newbie here...
I want replace an old 2 way dimmer switch for a 2 way rocker switch but never done it before...

I've had a look at the old dimmer switch (see photo) there doesn't seem to be any markings on the back such as L1/L2 and com?

 

[riveralt]

You haven't given us a good enough picture of the wiring of the old dimmer.

Photograph the back of the dimmer with the wires in place and visible.

It looks like you have a strapper (brown cable) between the the two commons - one of which includes a red cable which is the live in.
The other two cables will be your L1's.
It is likely that the dimmer's layout from gang one is inversed i.e. common at the bottom on the one gang and at the top on the other gang.