Reduce or cancel parking charges (7)
I believe the answer is:
deplete
'reduce' is the definition.
(I've seen this before)
'cancel parking charges' is the wordplay.
'cancel' becomes 'delete' (synonyms).
'parking' becomes 'p' (abbreviation on road signs).
'charges' means one lot of letters goes inside another (charge can mean to charge into something).
'delete' enclosing 'p' is 'DEPLETE'.
'or' acts as a link.
(Other definitions for deplete that I've seen before include "Drain" , "Use up, exhaust" , "Exhaust (stocks)" , "Spend" , "Empty, reduce, exhaust" .)