I have Lightroom on both Mac and PC. The upgrade to 5.7 from 5.6 worked fine on PC but not on Mac. When I get a popup or go to upgrade on the help menu, I click on upgrade but the link takes me to a 5.6 download which I already have installed.
Try this one:
Adobe - Lightroom : For Macintosh : Adobe Photoshop Lightroom 5.7
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