Transition altitude change

[ACA034137 37]

Hey all, quick question:

 

If I take off out of North America (transition FL180) to the UK (transition FL060), at what point should I be changing the transition level in the FMC? On entering UK airspace? On descent?

 

Regards-

[nrcrate 40]

The one for your climb is in your PERF INIT page, and the one for descent is on your Descent Forecast page.