Church features mostly cleaned up (4)
I believe the answer is:
pews
'church features' is the definition.
'mostly cleaned up' is the wordplay.
'mostly' means to remove the last letter.
'cleaned' becomes 'swept' (sweeping is a kind of cleaning).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'swept' with its last letter taken off is 'swep'.
'swep' back-to-front is 'PEWS'.
(Other definitions for pews that I've seen before include "Church benches" , "Church seats" , "Church seating" .)