Http To Https without Losing any seo value

We had to get a SSl cert on our site and we just beginners here so we wanted to find out if anyone can send us to a exact tutorial or give us a quick guideline for switching our site over. We have a ton of SEO we investing in for the Http site and would like to not lose it. I know that there is a way for us to forward those over to the Https and thought I would ask you guys for help. Thank you so much in advance.

We found this article: https://yoast.com/move-website-https-ssl/ but wanted to make sure if there was anything else we need to do.

Also what server changes we need to do as well? Its all over the place on the net about using SPDY but our Apache server cant do that but can if we add litespeed. I read tho alot of plugins conflict with litespeed. errrr so much to do on this.