To add a profile photo to Twitter, go to your account settings by clicking the gear icon, select "Profile" from the menu, and click "Change photo." You can then upload an image from your files, zoom and position it as desired, and click "Apply" to save the new profile photo.

1. HOW TO: Add Your Profile Photo to Twitter
Step 1: Click on the Settings icon in the
upper right corner of Twitter. It looks
like a wheel or gear.
Step 2: Click on Profile in the menu on
the left side of the page.
Step 3: Click on Change photo.

2. HOW TO: Add Your Profile Photo to Twitter
Step 4: Click on Upload photo. A file
window will open automatically.
Choose an image to use from your files.
Step 5: Position and size your photo by
using the slider bar to zoom in/out and
clicking and dragging your photo to crop.
Step 6: Click Apply and you’re done!