Ne help about putting picture in discussions!!!

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I have put wrong picture in one of the response I gave, which wasn't related to that topic. Before submitting I realise that I put wrong picture and when I wanted to change I couldn't as I didn't know how to change as I couldn't see any option to change that picture.. Do you know how to change picture before submiting discussion ( I know it's nt possible when discussion has been submitted)??? PLZZZZ HELP...... Thanx in advance