First, get a proxy address from a free list
https://www.proxynova.com/proxy-server-list/
http://geonode.com/free-proxy-list
Then, Open Network Preferences… -> Advanced… -> Proxies tab -> Check on ‘Auto Proxy Discovery’, ‘Web Proxy (HTTP)’, Secure Web Proxy (HTTPS) with Host and Port get on proxy server list link above -> Ok -> Apply
Go to https://www.myip.com to check new IP