This is for a pre 2005 fabia, but I would assume the newer ones are very similar.
If you take a small flat head screw driver you can pry it out gently. There's four small clips holding it in, similar to the clips that hold the small speakers in place. But, if your replacing it you don't need to worry about braking the clips. They are very brittle. Then all you need to do is take the connector out from the bottom. When you get a new one just plug it in and fit it back in place. You wont need any tools as it just clips in. The switches are pretty expensive (I've heard people buying them for £50!) so I would look on ebay. Just type in 'fabia braking' and email a seller to ask if he's got a switch. If your lucky like I was, it'l only be about £5 :) hope this helps.
Mr D
January 2011