It's easy to do. You 


If you need to edit details / delete a flight which is in the trip, you need to split it and then edit each flight. See more here how can you split trips.


iOS

Edit trip name.

Swipe trip left and tap on the blue button.


Re-name it


Edit flight details. 

Swipe flight left and tap on the blue button


Then you can edit flight details (as well as it's name)


Android

Edit trip name.

Tap & hold the trip and select the Edit button.


Re-name it


Edit flight details. 

Tap & hold the flight and select the Edit button.


Then you can edit flight details (as well as it's name)