Go to your profile by clicking on your name. In the right hand corner, you'll see a box. At the bottom of that box, it says edit profile pic. (or something) click it, choose a photo, crop, and save, and there you go.
^ Could just check the answers to the last two times you asked this.
To see replies to your post, click the "Comments" link underneath your post. This is probably not the most useful advice ever, as you wouldn't be able to read what I've written unless you knew this already. :D