What a change it makes to one's winnings! (8)
I believe the answer is:
cheating
'one's winnings' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'what a change it makes' is the wordplay.
'change it' anagrams to 'CHEATING'.
But, I'm unsure how the anagram is indicated.
'to' is the link.
Can you help me to learn more?
(Other definitions for cheating that I've seen before include "Swindling or deceiving" , "Acting unfairly" , "Change it for playing unfairly (8)" , "Swindling or defrauding" , "Acting dishonestly to gain advantage" .)