If your wireless connection is not working these are instructions to reset the Wi-Fi settings
Trash Existing Wi-Fi Preferences in OS X to Start Fresh.
Mac, Apple, OS X, Wi-Fi, wireless
/Library/Preferences/SystemConfiguration/
If your Wi-Fi works now, great, but for most users, you’re not quite finished yet! Now you need to create a new custom network location.
(This information is copied from: http://osxdaily.com/2015/10/16/fix-wi-fi-problems-mac-os-x-el-capitan/)