How do I wire a light controlled by two switches?
You need to connect the switched live to the brown wire in the new fitting and the neutral to the blue wire. The neutral will be one of the black wires. The switched live may be red, or it might be a black wire in one for the T&amp;E cables (though it should have red tape or sleeving on it if it is...).

You might need look at the switches to try and figure out which cable is which. A typical arrangement for two-way switching is shown here (I've linked rather than inline-display the image for copyright reasons).

I'd hazard a guess that the two cables with the red and black joined are the feed coming in and going out to the next fitting on the circuit - but don't take my word for that, please check that for yourself.