Drs Appt and how do I change my due date on here?

I finally had a Drs appointment the Dr was so nice and very pleasant, the desk staff much friendlier than last time but due to my irregular cycles the estimated due date was off my exactly 1 month to the day! Instead of Aug 2 my due date it Sept 2 and I can't find where to change it!

I was nervous going into my appointment, other than having a hard time sleeping and constant exhaustion I have almost no symptoms and I was kind of getting nervous that it was a false positive and something was wrong so when she found the baby and we saw the heart beating and heard the rhythm I was a mess of tears. It was so amazing the baby even wiggled some on ultra sound.  We got a picture I can't wait to share (s)he already looks like a baby just with a large head. Every measurement they did came out at 9 weeks and 1 day yesterday!  It was an amazing experience and even though after the office canceling my first appointment on me I had to wait 2 weeks longer to see our baby at a late enough time my husband could make it I am soo glad he was there and wouldn't have traded it for anything in the world! I might even be grateful for those 2 weeks our baby probably would have been a little harder to make out on our own with out the extra growing time!  I am already excited for my next u/s! It is on February 16th its an ultra screen with blood work and what not.  I meet the midwife on the 13th to go over all the medical history and dos and don'ts. 

Anyway if you could just tell me how to change my due date that would be awesome! Thanks!!!!