Q: Yosemite Internet Issues

I'm having sporadic trouble connecting to wifi networks on my iMac 10.10.5. Sometimes it works fine, then for no apparent reason, won't rejoin same network. Sometimes it looks connected, but won't load anything. This has happened on 2 separate networks, whilst my laptop and every other device connects fine. There is no issue with distance from the router, etc.

I would like to follow the suggestions in this article, but stumble at the first stage - I can't see any folder called SystemConfiguration. It just isn't there.

http://osxdaily.com/2014/10/25/fix-wi-fi-problems-os-x-yosemite/

Any suggestions greatly appreciated!