I'm not sure what you mean about drag the theme across to it. To change the Theme click "Edit Layout" then under "Layout" click "Change Theme".
You resize the page using the mouse. To change width put your mouse on the out side of the frame and drag. Each part can be resize to for example the header, body and footer can all be different heights. Place the mouse at the bottom of the part that you want to bigger or smaller. The mouse icon will change to left arrow with two bars with a right arrow (width) or up arrow with two bars with a down arrow (height).
Get started on tailoring layouts for FileMaker Go with our free FileMaker Go Toolkit!
Optimizing a FileMaker database for iPad or iPhone
Free Open Template with iPad and iPhone layouts
Mark's most recent collaboration with FileMaker, the How To Guide – Designing Faster iOS Database Apps – describes best practices for designing FileMaker Pro database applications for optimal performance on iPhone and iPad.
Please Note that a bug in FileMaker 12 will cause your filesize to increase each time you change a layout to a different theme. It's a good idea to use a copy of your file that you intend to discard for trying on different themes to find the one you like. Then select just the final theme for your layout in the development copy of your file.