To post the profile pic, go to the UserCP link at the top of the page then choose "edit profile picture". From there you can put in the information for your pics location (you should have already uploaded it using instructions above) and save it. There is a size restriction on your profile pic so if you're having trouble, your pic may be too large.
You might have been talking about the small pic under your name in posts. This is found under "edit avatar" in your UserCP. This pic also has a size limitation and is uploaded the same way as your profile pic. Hope this helps.