How do i change an old fashioned double light switch for a modern one?

the one in place at the moment has one of each red, yellow and blue wires at the top and one red and one black at the bottom
How do i change an old fashioned double light switch for a modern one?
Just go to the hardware store and buy one and follow the instructions. Its not difficult, just remember to turn off the power at the circuit breaker.
How do i change an old fashioned double light switch for a modern one?
It sounds like you have a single pole switch on the bottom and a 3 way at top. That may be a hard switch to find if thats the case. EIther way, Note all the wires locations before starting. If you have a tester, see if 2 of the three wires are hot on the top switch or if another switch controls the same light. This will help you determine what to buy.
Dont risk it - Get a licenced sparky
Is this double switch in a single gang box? Does it control two separate lights? If so it is not that way because it is an old design. It is that way so the electrician could fit two light switches in a place normally designed for one.

Unless you are prepared to do a lot more work, like replacing the single gang switch box with a double gang, then you would be best to leave the switch alone as long as it's doing it's job.
buy new switch remove old while noting locations of wires and simply reinstall new one

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