The remainder must be changed, on the quiet (5)
I believe the answer is:
stump
'the remainder' is the definition.
(thesaurus)
'must be changed on the quiet' is the wordplay.
'be changed' is an anagram indicator.
'on' says to put letters next to each other.
'the quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'must' anagrammed gives 'stum'.
'stum'+'p'='STUMP'
(Other definitions for stump that I've seen before include "Cricket stick" , "Small remaining part; cricket item" , "Part of a felled tree that's left in the ground" , "Wooden leg" , "Flummox" .)