• chmod 755 file Changes the permissions of file to be rwx for the owner, and rx for the group and the world. (7 = rwx = 111 binary. 5 = r-x = 101 binary)
• chgrp user file Makes file belong to the group user.
• chown youself file Makes youself the owner of file.
• chown -R youself dir Makes youself the owner of dir and everything in its directory tree.

You must be root or suoder to change the permission