Not able to extract files to the icons folder

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http://askubuntu.com – I downloaded some icons for Ubuntu from a site as a tar.bz2 folder. Now when bi try to extract the icons to my icons folder in the system i am getting the following message- Extraction not performed You don't have the right permissions to extract archives in the folder "file:///usr/share/icons" How can i copy the icons please help me (HowTos)