CEDET

Well, of course, I have ECB.

Loading /usr/share/emacs/site-lisp/site-start.d/ecb.el (source)...
ECB 2.40 uses CEDET 1.0pre7 (contains semantic 2.0pre7, eieio 1.2, speedbar
<unknown version>).

When loaded emacs -Q, I could load cedet without problems.
The old cedet is installed under /usr/share/emacs/23.2/lisp/cedet
So how do I upgrade my cedet to the newest version?

I haven't seen this problem. Are there other init files on your system
where CEDET is being loaded for other reasons? You can test like this:

emacs -q
M-x load-file RET /home/me/cedet/common/cedet.el RET

where you replace the path with your location of the CEDET init file. If
that works, you should check all your init files to make sure that CEDET is
not being used before your cedet init lines.

Check your .emacs, .emacs.el, init.el, or default.el, and anything else
that might be going on from your system.

Yes, it happens for me too. Mine is saying
Loading /home/michalp/code/cedet-1.0.1/common/cedet.el (source)...
progn: CEDET Version 1.0pre7 already loaded.
I didn't explicitly install cedet before and want to make sure I run the
latest version.