When I take a picture, it prints on the top half of a 8-1/2 x 11 size page. How can I take pictures that fill the page? 

There is no direct way to change the size of the picture from within STAAD.Pro. However here are a few options that you may find useful

Option 1

1. Before taking a picture, please ensure that the model is
   zoomed in sufficiently so that it fills up the space within the picture border as far as possible.
2. Take the picture and include that as part of the report using the Report Setup.
3. Go to File > Printer Setup and change the orientation to Landscape.
4. Go to File > Print Preview Report to check whether it looks satisfactory or not and if so, print it.

Option 2

1. You may copy the picture by going to the menu option Edit > Copy Picture. You can then paste the picture in MSWord or Excel or Paint.
2. Adjust the size of the picture using the tools available within these applications and take a print from there.