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At the moment the most popular downlighters are mains powered GU10 leds and the easiest dimmer to fit is varilight v-pro. The v-pro has several modes and you can adjust the low and high point. You can buy them as a separate module and retro fit them in your existing dimmer switches to save a little money.
You also need to check the height of the ceiling space as there is no real standard size for downlighters. Downlight.co.uk is a good source for quality units, avoid B&Q etc they will just make your job harder.
You could do it yourself but you need to consider the roof space and the temperature these lights get to. Also, you'll have to install a transformer as the normal lighting ring voltage will cause LED bulbs to flicker or die.
Depending on your skill level, you might just want to get someone in.