If you mean the ones with a smooth cover at each end, there is a small cutout on each one which you use a small flat bladed screwdriver to pop off, and underneath are the collars at the end of the fittings which press inwards towards the middle, and the pipe pulls out.
I new I could rely on you Damian, they are the push fit black ones similar to the domestic 15m copper ones, I am not aware of any cutouts, looks like a outer ring with a gap before the main body of the connector, any good ?
The inner ring is the collar which if you press it towards the middle of the fitting and pull the pipe with the collar compressed, the pipe should come out.
at the second item, a 12mm elbow, you will see the actual elbow, on each end is a wider band of plastic, then a thinner band, then a smaller protruding band (they are all rings), it is the small inner one which you compress as you pull the pipe out.
To refit, just push the pipe into the fitting as far as it will go. It automatically locks in