Need help with flash document background size

Hello-
I started out with a 776x700 document size and I am trying to change the dimensions on my flash document.
I changed the size to 766x900 and the background didn’t center, so he majority of my information is at the top.
I want to move everything (everything in my timelines and layers) down so that there is space on the top of my document and not on the bottom(which is what happened after I changed document size).

Is there anyway to do this?
I have tried selecting all the layers and moving them down, but that creates problems in my motion tweens.

Help?!
I hope I explained this well enough to get some help