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Then you can download them from your Mac mini, and copy installer to your MBP to upgrade.
 
Somehow the OS knows if the installer file is somewhere on the device and won't let you download another. It might be hidden away somewhere
 
Installesd.dmg, install OS X El Capitan.app

Your issue might not be because of this "feature"
 
The installer should be in your Applications folder, but if you ran it, it would erase itself.
 
i don't see how. i have never dowloaded it. what is it called so i can do a search of my machine?
H
It will also show "Downloaded" if you have saved the installer even to an external drive you have attached. So make sure you check there as well as the /Applications folder others mentioned.
 
If you've ever downloaded the El Capitan installer from the App Store to your iTunes account, go to the App Store app, and then to the Purchases tab. Find the OS X El Capitan item and click on the DOWNLOAD button. If it's greyed out and says "DOWNLOADED", it's on your system somewhere.

appstore.png

Do a search in Finder (⌥⌘ SpaceBar) and look for INSTALL. The file is called "Install IS X El Capitan.app".

install.png
 
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