On January 2017 Mozilla Firefox announced that it would it would categorize and display all the http format websites as not secure, followed by Google making similar announcement this year.
This announcement by two of the most used web browsers makes it necessary for all the major corporations to upgrade from existing http certification to https.

As of now more than half of all the websites worldwide lack the https secured encryption
Back in 2014 Google openly announced that https certification is an important factor which is used for ranking of websites. It is rare for Google to openly announce a criterion for ranking.
With increasing security threats in the internet it becomes more than important for website to undergo the https upgrade.

First of all the corporation must get a SSL security certificate and install in the web servers of the website.

Post certification and its installation all the links of the site must be upgraded from http to https, and the new links must be tested efficiently to avoid any server failure due to https upgrade, external resources such as Plugins, CDN (Content Delivery Network) should be upgraded accordingly. If the issues from external resource still occur one can either host the resource directly from the website or another host if possible.

HTTP/2 could also be used to ensure that the website could handle multiple request simultaneously
The SEO must not be neglected during all this customization, the SEO must be optimized to ensure that every external link directly connects to the newly customized website.
Customer application such as word press and magneto would help in ensuring that there are https redirects automatically conducted by the websites.

HTTS (HTTP Strict Transport Security) would ensure that all resources of the website are accessed via https; this ensures that there are no security loopholes in the website ensuring that the website is not vulnerable to hackers or bots.
With all these changes the website would become more secure and would help in improvements of Google ranking and thus benefiting the website.