1. Open up a terminal and go to your home directory
2. At the terminal, copy and paste the following command:
  cvs -d:pserver:anonymous@tinyos.cvs.sourceforge.net:/cvsroot/tinyos login
3. When asked for the CVS password, simply hit Enter
4. Now, copy and paste this command:
  cvs -z3 -d:pserver:anonymous@tinyos.cvs.sourceforge.net:/cvsroot/tinyos co -P tinyos-2.x
  Make sure that the entire thing shows up in one line. 
5. The above command will download a number of files from the CVS repository. 
6. Once it is done, type ls
7. You should now see a directory called tinyos-2.x in your home directory. We want to replace the default tinyos root (/opt/tinyos-2.x) with this new distribution. 
8. Rename your existing TOSROOT directory to something else:
  sudo mv /opt/tinyos-2.x /opt/tos-old
    When asked for password, type in your password
9. Now, move the new tinyos directory you downloaded from CVS to /opt:
  mv tinyos-2.x /opt
10. You are all done! :-)