我要退货. I'd like to return this. / I'd like to get a refundonthis.
    我想要换这个东西. I'd like to exchange this.
　 A: Excuse me.I'd like to exchange this blouse. 对不起,我要换这件衬衫.
    B: Whats the reason? 什么原因?
    A: Its the wrong size.尺寸不对.
    B: Do you have the receipt? 你有收据吗?
    A: Yes,I have.是的,我有.
    B: Go ahead and pick up the center size and bring it here,please. 请去挑尺寸合适的来.
    A: Ok, where is the fittingroom? 好的,试衣间在哪?
    B: It's behind you. 就在你后面.