I purchased Lightroom 4 for my Powerbook from the Apple store. I don't see any way I can register the product with Adobe or upgrade it to Lightroom 5
To register your copy of Lr, you have to create an Adobe ID, and afterwards you can register your serial number with them.
WIth regard to upgrading, go to this page:
about halfway down the entry for LR gives you the opportunity to buy an upgrade to v5.
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