How do I change document sizes?

Any help will be appreciated.  I have a pdf document that has two (8.5" x 5.5") postcards on it in a "2 up" style on a 8.5" x 11" page.  I want to effectively enlarge both post cards to 9" x 6.25".  I am willing to live with removing one postcard from the page in order to accomplish this.  Can someone help me?Image may be NSFW.
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