For most average users and you are wondering which to take:
On the canister, there's a "clean" button which will activate steam to clean the assembly, it should be done after each cup. After than you can place the canister with the remaining milk back to the fridge
Twice a week, the tank should be emptied and thoroughly cleaned, it's quite easy to dismantle but you may want to buy a tiny brush to clean the tube or replace it once a year.
For individual frothers, they have to cleaned after each session.
You have to do it every time, after you use the milk frothing function on the lattissima.
Each cup do once. Hold the clean button for 10 secs till the water run clear.
This is to prevent milk from clogging which may lead to contamination.