Article in English: It's a green app with a white text bubble that's typically found on your home screen. If the app opens within a conversation, tap the "Back" arrow (<) in the upper-left corner of the screen. It's in the upper-left corner of the screen. The buttons are on the left side of the screen and will turn blue as you select conversations. Conversations can use a lot of data, especially if they contain multiple messages with media like photos or videos. It's in the lower-right corner. All of the selected conversations will be removed from your device.

Summary in Chinese:
打开“信息”应用程序。 点击编辑。 在想要删除的对话旁边点击按钮。 点击删除。