For the most part, you should be fine. Just upgrade all your URLs from "http" to "https" in the control panel and includes files.
Insert both http and https variations of your URLs here:
Control Panel > Primary Settings
Domains for HTTP Referer Check
Update your "Contact Us" URLs to also use https, is using a link, rather than an email address.
With UBB.threads 7.5.x, you will run in to
several very few cases where "https" will not process as a valid URL, so in that case, just use the "http" version, and let your .htaccess forward things for you. This is not a major issue. Its only a minor hiccup that you might not even notice. Your forums will still run correctly. -- Mostly just in the user settings for, "your website address" and some BBCode translations.
For bonus points, you could run a SQL query to replace all "http://www.yoursite.com" links to "https://www.yoursite.com" in POSTS, PM/PT, PROFILE COMMENTS...etc.
Also, dont forget to resubmit your website and it's new https urls to search spiders, and the Google Search Console or Bing Webmaster Center if you use either of them. If you have ads on your website, update their code to use https variations of their code - for example:
https://support.google.com/adsense/answer/10528?hl=en
