Just rooted.
root@traceback:~# whoami
root
root@traceback:~# id
uid=0(root) gid=0(root) groups=0(root)
root@traceback:~#
Hints :
Foothold : Examine the home page and source code. Google combination of words.
User1 : Easy… Just a reverse shell away.
User2 : Read carefully whats in user1’s home page files. Google about how to execute commands using what you have. Man pages will help you.
Root : Look for whats going on in the system. Examine the processes and google about how they work. Once you understand, its easy 
Feel free to pm for help.