Go under your user CP (Control Panel)
1-Click on Edit Avatar
2-Select Use Custom Avatar
3- you can Option 1 - Enter the URL to the Image on Another Website or
Option 2 - Upload Image From Your Computer
(copied from MrMuslim)
But this option probably won't be open to you until you hit the approx 40 post mark brother, so until then please continue contributing to the forums and it should open up inshaAllaah.