Slow, losing heart and urge to change (6)
I believe the answer is:
switch
'change' is the definition.
(I know that change can be written as switch)
'slow losing heart and urge' is the wordplay.
'losing heart' means to remove the middle letters.
'and' says to put letters next to each other.
'urge' becomes 'itch' (I've seen this in another clue).
'slow' with its centre removed is 'sw'.
'sw'+'itch'='SWITCH'
'to' acts as a link.
(Other definitions for switch that I've seen before include "Change over - long twig" , "Device for changing electrical connections" , "turn" , "It may be thrown" , "Change or exchange" .)