El Capitan

If you have a specific problem please post about it. You have given us no information with which to help you. See Writing an effective Apple Support Communities question for help in posting a good question. These are not general discussion forums. You need to post a specific question describing your particular problem and everything you know about the problem at this point. This includes error messages, etc.

shut down

detach all external devices from your computer (except mouse and keyboard)

reboot intosafe mode

go to terminal

type

open $TMPDIR../C/

delete the folder

com.apple.appstoreclose terminal open AppStore

download El Captian

it is advised you make a full backup before upgrading your OS

it is preferable to use a wired connection to your router or cable modem instead of wi-fi, and to suspend any other device on the router that is downloading or streaming .

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