Do this by tapping the white speech bubble on a green background icon. It should be on one of your Home screens. This is in the top left corner of the Messages screen. If you have a conversation open, tap < in the top left corner of the screen to return to the Messages menu.  This is in the bottom right corner of your screen. Your selected messages should now be gone.
आईफोन मैसेजेस को खोलें: Edit पर टैप करें: आप जिन भी कन्वर्सेशन को डिलीट करना चाहते हैं, उन सभी को चुनें।  Delete टैप करें: