Software purchased through the Mac App Store can be downloaded again any time you need, on the same or different computers.
-Open the Mac App Store by clicking its dock icon.
-Click on the “Purchased” toolbar button in the App Store application after the download has begun.
-You will see a full list of all the software you have purchased, along with the current status of each purchase.
-You may need to delete the application you want to download again. To do this go to navigate to [Your User Name]/Applications, locate the app you want to remove, and drag it to the Trash.
-You can then download the software again. This is the equivalent of uninstalling and reinstalling software purchased through the App Store.