If you're looking to update a previous thread, you can just make a new post in your old thread, which will bring it to the top of the list (and keep this post with any previous discussion/information), rather than making a new thread.
You mean how do you add on to your old thread? You just post a reply in the thread like you did earlier in the week: TRANSFORMERS PNG/RENDER/TRANSPARENTS Or are you asking something else?
What exactly are you asking for? Your other thread is in the Requests section. Just add a new post to it rather than start a thread in the wrong section.