And if I unistall .. packages like the latest g++-4.7 everything
is reset and can reinstall it or install older versions ?
You are supposed to have all the versions installed at the same time.
They have unique file names / locations : No conflicts.
And no reason to uninstall a compiler.
Example Debian Wheezy : /usr/bin/ g++-4.4 g++-4.5 g++-4.6 g++-4.7