If you are needing to change the aerator on your tap the removal of the old aerator can actually be done by using the new piece.

Carefully remove the piece from your tap shown here (we suggest wrapping some plastic wrap around this if using tools to minimise scratching)

And then when fitting the new aerator piece, you can connect the old two together as shown below, twist, and it'll pop out and you can pop new new one back in!