1. Open screenshot file.
2. Open a new MS paint window, make the available screen as small as possible.
3. Go to screenshot file and select the spot where you wish to put as your picture. Copy it.
4. Go to the new MS paint window. Paste it. The available spot for the info should be bigger now, to accomodate the new stuff.
5. Save it, upload it. Yays.

I suggest getting something better than MS Paint though. It's terrible. I'm sure there are some free photo editing software out there. I happen to have photoshop already so it's great.