How to change page size
When, for example, users use Powerpoint to make posters for their final projects, they will often not realize that the default page size for a powerpoint slide is very small. The option to change it is under the Design tab, first option on the left. Usually they will want to change it to 24x36.
When users send us posters made in power point that are not the correct dimensions, you can try to change it for them like this. However, in the likely event that this messes up their poster, SEND IT BACK TO THEM. It is not our job to fix their posters.
As a side-bar, also recommend that they be using Publisher for making posters since Powerpoint really isn't made to make big print-able posters like that in the first place.