As title really, do i need to take something off the existing wheels and put on the new ones? How does it work?

Nope, just press the reset button if needed.

1 minute ago, Berisford said:

Nope, just press the reset button if needed.

So sensors aren't in the wheels on the fabia?

No, it monitors the speed that each wheel rotates.

Deflating tyre = smaller radius = faster rotation = alarm raised.

17 minutes ago, alan4856732 said:

No, it monitors the speed that each wheel rotates.

Deflating tyre = smaller radius = faster rotation = alarm raised.

Spot on.  ABS sensor.  No special valves or similar. 

Re Reset TPMS & Pressing the Button.

 

Yes Reset as you fit different tyres / wheels, Spare Wheel, but also when you are regularly checking tyre pressures, or resetting as weather changes, 

or you adjust if carrying more passengers / luggage etc.

Check TPMS from time to time as per 'Owners Manual'.