I never touch the rear clips.
You will need a flatblade (the smaller the better) make sure the switch is in the off position so the brightly coloured bottom is sticking out the housing more (let's say you have a DC07 in yellow and silver for example).
Get a tiny flat blade, stick it in the back of the yellow switch from one side, pry it out. Now do the same with the other side, I can guarantee you it'll work 99.9% of the time.REASSEMBLY:
Making sure the wires are seated firmly in their places. The blue wire must be tucked in properly in the left hand side gap and the switch wired up with the prons at the back, this will stop the spade connectors getting in the way when fitting the cover.
To fit the cover, make sure the switch is pressed "on" then using two hands, place the housing nicely from the bottom first and holding the yellow button up at the same time. Then press down, till you hear a satisfactory click.
To make sure it's deffo in for sure, look at it from a bird's eye view. If the switch wobbles about, it's not on correctly, there should be no gaps because Dysons are engineered nicely