• The download file for Catalina is over 6GB in size, and you'll need 15GB to 20GB of free space to finish the installation. Click the Apple menu in the top left corner of your screen, pick About This Mac, and then Storage to see how much free space you have on your hard drive. Here you'll be able to control your storage and, if necessary, free up some space.
• If these problems aren't the source of your Catalina problems, check to see if the installation file was corrupted or only partially downloaded. Search for the Install MacOS 10.15 file in the Finder menu and delete it. Then reboot your system and try to re-download the necessary files from the Mac App Store.
• If you're still having trouble, try logging in and out of your App Store or iCloud account. After you've downloaded the file, it should urge you to run the update. If not, simply look for the Catalina installation file on your Mac's hard disc and double-click it to begin your descent into the dark side of your Mac.

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