You can consider expanding on your original forum postings extensively by adding photos, discussions, thoughts, etc. before republishing it onto your website, and by extensively, I mean adding around 300 to 500 words to the original content.
Having some quality inbound links pointing to the republished content on your website will tell search engines that the republished content is actually more useful than the forum postings. This shouldn't be a problem if the republished content is more useful and valuable for visitors. You may need to share it on relevant social media sites and with influencers if your website is still very new.
Going back to your forum posts and editing them takes a lot of time and I would rather spend that time working on my own website.