Exchange or swap (6)
I believe the answer is:
switch
This clue is a double definition.
'exchange' is the first definition.
(I know that exchange can be written as switch)
'swap' is the second definition.
(I know that swap can be written as switch)
(Other definitions for switch that I've seen before include "turn" , "Device for changing electrical connections" , "Change or exchange" , "Change round" , "Device for opening or closing a circuit" .)