A couple of different ways…
1 – WashU Speedtest (Recommended method)
http://speedtest.wustl.edu/speedtest/
2 – Speedtest By Ookla
https://www.speedtest.net/
3 – Google Speed Test
https://www.google.com/search?q=google+speed+test
4 – Cloudflare Speedtest
https://speed.cloudflare.com/