If you are buying release keys from Halfords, reserve them online before you go otherwise
we will rape you on price.
http://www.halfords.com/webapp/wcs/..._productId_734063_langId_-1_categoryId_265879
Online - 99p
Instore - £5.99.
How does it work? Basically there is a cage that is held into a recess in your dashboard (usually designed for the stereo, so always fit the cage that comes with the stereo). There is a catch or clip on either side of the cage that grabs the stereo as it is slid in.
Release keys slide through the front of the original stereo but actually end up sliding down the side of the stereo's chassis and pushing out the catch from the cage, release keys also have a notch in them that usually grab the stereo that allow you to pull the stereo out once the catch has been released.
As said the same result can be achieved using allen keys, bicycle spokes, wire coat hangers etc. as all you want to do is push out the catch. The only difference been here is trying to pull out the stereo. If you have a strong tool like an allen key you can push the allen keys outwards and try pulling.
In regards to the steering wheel controls, you need to make sure the new stereo is compatible with stalk controls and also purchase the relevant patch lead. The connector for this though (at least on my car) is behind the clock and temperature display and requires removal of the top section of the dash.