High Sierra upgrade slowed system, how to downgrade to Sierra 10.12.5

Last week a new update for Sierra was automatically installed on my computer, which really messed up my system, a 2013 Macbook pro, upgraded with SSD hard drive and 16GB ram. Everything was freezing and slowed down considerably, trouble staying connected to wifi. I felt like this was done to force users to upgrade to High Sierra which I did, but system is still much slower and lags terribly, much worse than last week when I was using 10.12.5. How can I go back to the previous version of Sierra?