Ok let me start off my saying this isn't the most detailed guide you'll ever read, but the major steps are here...any questions...just ask!! :P
This is the kit I installed which I purchased from here:-
Standard engine bay
Start by removing these 4 torx screws, the top left one is down below the maf sensor
Now remove the two maf sensor screws, the whole maf sensor fitting will be screwed into the new pipe with two screws provided.
Undo the flat head screw on the jubilee clip and wiggle the rubber pipe free from the stock air intake plastic housing
At this point just wiggle the whole intake housing free, no for needed, and pull upwards. Note: towards the front of the car the intake may need a little help from a flathead to be removed but again no force needed at all.
I then removed the two rubber holders shown below as I did not want them to fall out later and I stored them away with the stock intask system.
Now simply fit the new system by attaching the induction pipe and tightening the jubilee clip, attaching the maf sensor unit to the new housing and bolting on the kit to the pre existing hole at the front of the engine bay (most fiddly part of the whole install). Use a screwdriver to hold the bolt from turning from underneath and then a socket set to tighten the bolt on top
And now for the best bit:-
Hope this helps, like I said its not super detailed as I realised after I didn't take pics of all steps (initial construction of the kit, take out the stock airbox, doing up the holding bolt for the new system) but if you get stuck just ask. It's a simple install really...15 Mins work max!! Changed my mind about getting a blow off valve after hearing this!!
Also, feel free to check out my complete build thread for my Fiesta ST-2:-