If I take DAT on July, and if the score is not good, then can I take it again on Oct and is it going to be updated automatic so that the school will look at my new DAT scores after Nov ?
They'll know it's updated because AADSAS will say "sent X date" under mailing information after you add your new test information. If you do well then they'll take that into account, but by October it might be considered "late".
Case in point, I wouldn't retake until you're sure you're going to do well/better.