How to uninstall linux-backports-modules-alsa-2.6.32-21-generic from Ubuntu
To uninstall just linux-backports-modules-alsa-2.6.32-21-generic package itself from Ubuntu execute on terminal:
sudo apt-get remove linux-backports-modules-alsa-2.6.32-21-generic
Uninstall linux-backports-modules-alsa-2.6.32-21-generic and it's dependent packages
To uninstall the linux-backports-modules-alsa-2.6.32-21-generic package and any other dependant package which are no longer needed on Ubuntu.
sudo apt-get autoremove linux-backports-modules-alsa-2.6.32-21-generic
If you also want to delete configuration and/or data files of linux-backports-modules-alsa-2.6.32-21-generic from Ubuntu then this will work:
sudo apt-get purge linux-backports-modules-alsa-2.6.32-21-generic
To delete configuration and/or data files of linux-backports-modules-alsa-2.6.32-21-generic and it's dependencies from Ubuntu then execute:
sudo apt-get autoremove --purge linux-backports-modules-alsa-2.6.32-21-generic
linux-backports-modules-alsa-2.6.32-21-generic package information
Ubuntu supplied Linux modules for version 2.6.32 ALSA snapshots.
This package contains modules supplied by Ubuntu for Linux 2.6.32 ALSA snapshots from http://www.alsa-project.org/main/index.php/Main_Page You likely do not want to install this package directly. Instead, install the linux-backports-modules-alsa-generic meta-package, which will ensure that upgrades work correctly, and that supporting packages are also installed.
More information about apt-get remove
Advanced Package Tool, or APT, is a free software user interface that works with core libraries to handle the installation and removal of software on Debian, Ubuntu and other Linux distributions. APT simplifies the process of managing software on Unix-like computer systems by automating the retrieval, configuration and installation of software packages, either from precompiled files or by compiling source code.
apt-get is the command-line tool for handling packages, and may be considered the user's "back-end" to other tools using the APT library.
apt-get remove is identical to install except that packages are removed instead of installed. Note that removing a package leaves its configuration files on the system. If a plus sign is appended to the package name (with no intervening space), the identified package will be installed instead of removed.