I
noun
BAD : We can reduce the unemployment rate with a change of the economy.
GOOD : We can reduce the unemployment rate with a change in the economy.
BAD : I'm disappointed by all the changes of London.
GOOD : I'm disappointed by all the changes in London.
◆◆◆
Use change of when you mean that someone or something has been replaced: 'What the country needs is a change of government.' (= a completely new government)
When you mean that someone or something is now different in some way, use change in : 'The Prime Minister has made several changes in the government.'
II
verb
BAD : I took the camera back to the shop and changed it with another one.
GOOD : I took the camera back to the shop and changed it for another one.
◆◆◆
change/exchange sth for sth : 'I'd like to change this shirt for a smaller size.'