There's not much left but to change the title (6)
I believe the answer is:
little
'there's not much' is the definition.
I can't tell whether this defines the answer.
'left but to change the title' is the wordplay.
'left but' becomes 'l' (common abbreviation. I am not sure about the 'but' bit.).
'to change' indicates anagramming the letters.
'title' is an anagram of 'ittle'.
'l'+'ittle'='LITTLE'
Can you help me to learn more?
(Other definitions for little that I've seen before include "(Heroine of) Dickens novel" , "The Battle of ... Bighorn, Custer's last stand" , "Small in quantity or degree" , "younger" , "Not big, much or important" .)