Change speed with nothing to displace (6)
I believe the answer is:
depose
'displace' is the definition.
(thesaurus)
'change speed with nothing' is the wordplay.
'change' indicates an anagram.
'with' indicates putting letters inside.
'nothing' becomes 'O' (looks like zero - 0).
'speed' is an anagram of 'depse'.
'depse' enclosing 'o' is 'DEPOSE'.
'to' acts as a link.
(Other definitions for depose that I've seen before include "Remove from top position" , "Remove from power or testify on oath" , "Speedo (anag)" , "Throw out" , "Remove (from high office)" .)