moving directory structure up one level - how?

view story

http://www.linuxquestions.org – I wanted to install phpBB3 on a Debian Wheezy system, so I downloaded it to my Desktop, created a new directory which I called /usr/share/phpbb, and moved my downloaded (zipped/tarred) file to it. I then did an bunzip2, followed by a tar xvf. That created a whole file structure, which come to find out is all under a new folder called phpBB. I want to move the whole thing up one level so that it comes to live at /usr/share/phpBB3, thus eliminating the needless extra level I created when I made the directory phpbb. What are the steps (please spell out in painful detail) to accomplish this? (HowTos)