ive got the larger screen, and yes you take the oe one off before.

The rest i dont really know as it was on my bike when i got its!!

The black line in the left piccy it suppose to be the screen, it means you have the rubber tube which has a thread nut on the inside. Push it throught the hole of the new, longer brackets, then place a steel washer on the backside of the tube. Push the screen on to the front of the bike lining up the holes, slowly push the screw through and start turning, make sure the washer stays on. The metal thread will grab hole of the screw and pull in curling up the rubber in front of it, make sure the washer is as close to the screen as possible.

Hope this helps!

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Plough on