To edit your company profile, click on Profile > Company Profile on the top navigation bar. Click on "Edit".
Next, you'll see the "Photos" module towards the middle of the screen.
To upload photos, either drag pictures from your computer to the browser directly, or click the "Browse" link. You can select multiple pictures at a time.
When your pictures are done uploading, you'll be able to see them immediately.
If you're not happy with any picture, click the little gray "X" on the top right of the picture to delete it.
Click "Save" and you're done.