it is pretty easy, the how too was mine if you read it on here, the most difficult part of the whole change is having compressing the springs on the front.
just take your time, if your handy with a set of spanners it really isnt that hard aslong as it comes apart.
i have lowered 10 fiesta ST's now, most of them are on this site

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Red Escort 1.6LX
Then - Red Escort 1.4
Then - Silver Fiesta ST 170BHP
Then - White Fiesta ST MR200+
Now - Mitsubishi Evo IV Forged 2.3 500BHP
and Mondeo Mk3 2.0TDCI