一个人如果 have a change of heart，那意思就是此人对某事的态度或想法有了改变。
I know we agreed to get a new kitchen this year, but I’ve had a change of heart. I think we need a new car more.
Following public anger the government had a change of heart on their financial policy and decided not to raise tax rates.
You have to pay for gym membership a year in advance, but if you have a change of heart you can get a full refund for any complete months remaining on your contract.
表达 change one's tune 的意思是为了好处而改变看法或改变论调。这个短语多数情况下是贬义的。
So you support the management now? You’ve changed your tune. Only yesterday you were criticising them.
He didn’t like the proposal at first but changed his tune when he realised he would be entitled to a huge bonus.