Kindle books for android - choice of where to save?

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http://www.mobileread.com – I have a Nexus 7 with the kindle app on it. Which I find really good. Have subscribed to the Kindle and Kobo newsletters that notify me daily of free books. I have download lots for future reading. They go straight to my Nexus 7. However some I would like to go to the PC till I get round to reading them. How do I change the setting and how do I get them from the PC to kindle app on nexus 7 at a later date? (HowTos)