You don't really want to put your email address here in the forum.
you can reply to this thread by returning to the web page, or by email. Please don't start a new thread each time.
Back to the question, if things can stand scaling, one of the easiest methods of doing waht you want is to place the pages of your file into a new document made to the smaller size. For that, use File > New.. and set the size to 7.5 x 10.5 inches. Margins won't matter in this case.
Go to InDesignSecrets » Blog Archive » Zanelli Releases MultiPageImporter for Importing both PDF and INDD Files and download the script. See How to install scripts in InDesign | InDesignSecrets for how to set it up.
Once installed, open the Scripts panel (Window > Utilities > Scripts) and double click the script name to run it. It's pretty intuitive -- there are settings for scaling built in.
The other option, if the book can really stand having a half-inch removed from each side, is to go to Layout > Liquid Layout and rom the panel menu in the upper right corner of the panel choose Layout Adjustment and clcik the box to enable it. Next go to Layout > Margins and Columns and subtract half an inch from each margin, and finally go to File > Document Setup... and change the page size. This might work really well, or you might have a real mess (it depends on how things are snapped to the margin guides), so use a copy of the file to try it.
I will review.