Remove pins from plugs and gently pull out the wire. Pliers work better than teeth. I don't need to do this as I won't be putting the plug back on so I can just smugly snip off the annoying plug with scissors.
Decide if you are keeping or removing the sticky pad. Keep it - nice easy way to attach to ceiling. Remove it - goes flush to ceiling with no pad showing but not always easy to glue in place. I use a DeLuxe Modellers glue and a couple of spots of gel superglue to hold it while the other glue dries. Also be careful to put the cut out space for the wire which is now longer needed to the back otherwise I promise you it will annoy you forever and a day.
Thread wire through hole
With glue applied or sticky-pad in place, support light beneath, pressing the fitting to the ceiling and pull the spare wire through gently. Thread through the exit hole (usually at the back of the house and lay the wire in the groove. I just broke the wire on one light being too enthusiastic.
Et voila! One puny light in place. I hope to add strip lights under cupboards at the back of the room.
When the light is holding up under its own strength, smooth out the wire in its channel and cover the wire and groove with masking tape just to help keep it in place and to make a perfectly smooth area under your flooring. If you use thin paper flooring you may want to stick it to cardboard to conceal any bumps. Reminder - use a few pieces of thin double-sided sticky tape to attaching all flooring to floor so that in the worst case scenario you can remove the floor intact and peel off the masking tape and remove the light at any time in your house's lifetime, should you want to.
To strip plastic from the wires a wire-stripper/cutter works better than teeth or fingernails.
I test and test at every stage to check I haven't broken anything. Ironically this is the light whose wire I did snap. Just touch bare wires to 9V battery - any wire to any terminal.