Change of first name

Hi, I have an unique first name. This means that if people google me, they get to my LinkedIn profile and website. When I created my account, I used my complete firstname. Now I asked a question in one forum and I saw my complete first name. I editted my first name in my account details (shortened it). But the forum post still has my complete firstname. Can you change that? (Or even remove the forumpost, I will then add it again) Sorry for the inconvenience. Oh oops, even after the change, also this post displays my old (complete) first name.