How can i edit my post?

In the case of posts or replies which you've already made, there should be Delete and Edit buttons at the foot.

Clicking the Edit button enables you to change or add to what you've written. You can then click the Post button to accept the edit or the Cancel button to cancel it.

Clicking the Delete button deletes the post or reply entirely. 

Notice that if you're the original poster of the thread, deleting your first post will delete the whole thread including any replies that other people have made. If you do this, you won't be popular with people who've spent a long time on their replies!