Stumble heading off to change (5)
I believe the answer is:
alter
'change' is the definition.
(I know that change can be written as alter)
'stumble heading off' is the wordplay.
'stumble' becomes 'falter' (synonyms).
'heading off' means to remove the first letter.
'falter' with its first letter taken off is 'ALTER'.
'to' acts as a link.
(Other definitions for alter that I've seen before include "Change, make different" , "reform" , "Change, maybe later" , "Change or adjust" , "and 10 Across: Second self" .)