You can do whatever the system administrator allows you to do. Users aren't supposed to screw around modifying the system, users are idiots who need to be given permission to do things according to their ability and knowledge.
To administer your system, you must use the root account.
To change to the root account, use these commands from your user account. Note the change in the prompt.
[fancy@tinwhistle fancy]$ su -
Remember, whatever you command in root (it's the "god" mode. You can bless or destroy at your whim) usually gets done if enough system is left to carry out the command.
Sit on your hands and read at least 3 times before pressing the enter key when in root.
Linux Newbie Administrator Guide
Rute User's Tutorial and Exposition