Choose a new top (3)
I believe the answer is:
opt
'choose' is the definition.
(both can mean to pick something)
'a new top' is the wordplay.
'a new' is an anagram indicator.
'top' anagrammed gives 'OPT'.
(Other definitions for opt that I've seen before include "Have preference for something" , "Elect" , "Make a choice" , "Choose from pot" , "End or act of shutting" .)