let say i've choosen to install PHBB.
But later on i decided to remove it. This is what i'll do;
1. remove the directory where it was installed.
2. remove database and users which was created for it.

but, is there any better way?. at cpanel, removal script, etc?

Yes the way u hav described is exactly the same way cpanel uninstalls a script, I prefer to do it all manually using file manager and cpanel incase an error occurs int he cpanel script (uninstallation).

Yea I Use CPanel To Delete Pre Installed Scrips... But I Like Deleting them manualy better.. then you know that they are gone, and aren't wasting space.

Deleting the script manually with FTP is very slow as it has to recurse through all the folders.
Just use the cPanel/Fantastico uninstall script first, then check to see if it missed something.

There is an automated way to uninistall scripts using cpanel. It is located to the place where yuo installed the script. For example: you installed phpbb. then yuo decided to remove it. Simply click the phpbb button in the scripts and you can find the remove installation or if in the fantastico the word remove...

@wanhafizi : Im' rather surpized. I would first remove the database, and after that remove the datafiles, not the opposite.
@kenjvalip : I have a photo gallery not working any more after the last Astahost physical server change. And then, the automatic uninstaller in the cpanel does not uninstall, it simplay says "an error occured", which is normal because the script does not work because of server name bugs.
So, I will have to uninstall manually, and the precise method is something interesting to be known.
Regards
Yordan