Using command line
1-Backup the original icon (open a terminal ctrl+alt+t) :
sudo mv /usr/share/unity/icons/launcher_bfb.png /usr/share/unity/icons/launcher_bfb-back.png{codeBox}
2-Copy your chosen icon to /usr/share/unity/icons/ and rename it to launcher_bfb.png by the following command :
sudo cp /path (the icon path)/icon-name.png /usr/share/unity/icons/launcher_bfb-back.pngfor me it like that: sudo cp /home/djalel/Pictures/ubuntu.png /usr/share/unity/icons/launcher_bfb-back.png {codeBox}
Using file Manger
1-Open the file manger as root:
gksu nautilus{codeBox}
2-Rename the icon to launcher_bfb.png
3-Copy it to the folder /usr/share/unity/icons/
Before you paste the new icon just backup the old one by rename it to launcher_bfb-back.png logout & login again for the change take effect.{alertWarning}