LOL do we not have a sticky for this yet?
Ok, lets use an example of a LO who wakes at 7am, goes to bed at 7pm, and naps once per day at 1pm for 2hrs (you can adjust to your own times
Clock change happens between Sat night and Sun morning, so we start adjusting on a Thursday at nap time, where LO is put down at 1.15pm and woken at 3.15pm (instead of the usual 1-3pm). BT is shifted forward to 7.15pm.
On Friday morning LO is woken at 7.30am (if they wake earlier it's not a problem, but ideally leave them in bed until 7.15/ 7.30am if poss). They go down for nap at 1.30pm and wake at 3.30pm. BT is now moved back to 7.30pm.
On Saturday morning LO is woken at 7.45am (again an earlier WU is not a big deal but try to leave them undisturbed if poss). Nap is at 1.45pm until 3.45pm. BT is at 7.45pm. Parents put the clocks back as usual before going to bed on Saturday night.
On Sunday morning LO is woken at 7am (old 8am time!), put down for nap at 1pm - 3pm, and BT is 7pm (all these are new clock times).
If you are going to get confused, write it down as a daily plan - very useful when LO is taking more than 1 nap per day!
Don't worry too much if LO doesn't adapt exactly to the new times, these are an ideal but anything and everything can throw them out (teething, illness, overstimulation, travel etc.), so remain flexible
For the clocks going forward in Spring, you apply the same process, but this time you start on Thursday morning by waking LO up 15 mins earlier and carry on adjusting the day accordingly.
Hope this is helpful