Remove five hundred and switch position (4)
I believe the answer is:
doff
'remove' is the definition.
(I've seen this before)
'five hundred and switch position' is the wordplay.
'five hundred' becomes 'd' (Roman numeral for 500).
'and' means one lot of letters go next to another.
'switch position' becomes 'off' (I've seen this in another clue).
'd'+'off'='DOFF'
(Other definitions for doff that I've seen before include "Take off hat as mark of respect" , "Remove (e.g. hat)" , "Lift (one's hat)" , "Remove one's cap" , "Remove, hat say" .)