以切换到GDM为例，打开终端，使用命令：
sudo dpkg-reconfigure gdm
sudo dpkg-reconfigure kdm
切换桌面系统还可以用：
killall gnome-session //因为系统会自动重启gnome-session
sudo service lightdm restart //该命令会结束当前用户的会话，返回到登录界面，它的作用和注销差不多。但是它的缺点和上一个一样，无法保存用户在崩溃前尚未保存的数据。
删除gnome：
sudo apt-get purge --auto-remove alacarte bogofilter bogofilter-bdb bogofilter-common browser-plugin-gnash cheese cheese-common cups-pk-helper dconf-tools desktop-base ekiga epiphany-browser epiphany-browser-data epiphany-extensions evolution evolution-common evolution-plugins evolution-webcal fonts-cantarell gdebi gdebi-core gdm gedit-plugins gimp gimp-data gir1.2-accountsservice-1.0 gir1.2-caribou-1.0 gir1.2-clutter-1.0 gir1.2-cogl-1.0 gir1.2-coglpango-1.0 gir1.2-folks-0.6 gir1.2-gdesktopenums-3.0 gir1.2-gee-1.0 gir1.2-gjsdbus-1.0 gir1.2-gkbd-3.0 gir1.2-gucharmap-2.90 gir1.2-json-1.0 gir1.2-mutter-3.0 gir1.2-networkmanager-1.0 gir1.2-panelapplet-4.0 gir1.2-polkit-1.0 gir1.2-telepathyglib-0.12 gir1.2-telepathylogger-0.2 gir1.2-upowerglib-1.0 gir1.2-xkl-1.0 gjs glchess glines gnash gnash-common gnect gnibbles gnobots2 gnome gnome-applets gnome-applets-data gnome-backgrounds gnome-contacts gnome-core gnome-dictionary gnome-games gnome-games-extra-data gnome-icon-theme-extras gnome-icon-theme-full gnome-js-common gnome-panel gnome-panel-data gnome-session-fallback gnome-shell gnome-shell-common gnome-themes-standard gnome-video-effects gnotravex gnotski gnuchess gnuchess-book gtali hamster-applet iagno imagemagick imagemagick-common indicator-applet-complete inkscape libbabl-0.0-0 libblas3gf libbonobo2-0 libbonobo2-common libbonoboui2-0 libbonoboui2-common libboost-iostreams1.46.1 libboost-program-options1.46.1 libboost-signals1.46.1 libboost-thread1.46.1 libcapi20-3 libcaribou-common libcaribou0 libcdt4 libcheese-gtk21 libcheese3 libclutter-1.0-0 libclutter-1.0-common libclutter-gst-1.0-0 libclutter-gtk-1.0-0 libclutter-imcontext-0.1-0 libcluttergesture-0.0.2-0 libcogl-common libcogl-pango0 libcogl9 libept1.4.12 libevolution libgc1c2 libgdict-1.0-6 libgdict-common libgegl-0.0-0 libgfortran3 libgimp2.0 libgjs0c libglade2-0 libgnome2-0 libgnomecanvas2-0 libgnomecanvas2-common libgnomeui-0 libgnomeui-common libgnomevfs2-extra libgraph4 libgsl0ldbl libgtkhtml-4.0-0 libgtkhtml-4.0-common libgtkhtml-editor-4.0-0 libgtkmm-2.4-1c2a libgvc5 libilmbase6 liblapack3gf liblqr-1-0 libmagick++4 libmagickcore4 libmagickcore4-extra libmagickwand4 libmozjs185-1.0 libmusicbrainz4-3 libmutter0 libmx-1.0-2 libnetpbm10 libodbc1 libopal3.10.2 libopenexr6 libpanel-applet--0 libpathplan4 libpst4 libpt2.10.2 libseed-gtk3-0 libwmf-bin liferea liferea-data lightsoff menu menu-xdg mutter-common netpbm notification-daemon odbcinst odbcinst1debian2 perlmagick python-gmenu python-gnome2 python-lxml python-numpy python-pyorbit python-uniconvertor quadrapassel sound-juicer swell-foop synaptic unixodbc
不过看起来要删除的内容就太多。
安装gnome3
http://jingyan.baidu.com/album/e2284b2b441992e2e6118d8e.html //百度百科 卸载gnome
http://www.ibirchs.com/html/41.html //一个家伙写的安装
http://ubuntugnome.org/download/ //官方下载
http://www.gnome.org/ //官方介绍
http://blog.csdn.net/jcjc918/article/details/25547983 //kubuntu 的初始化设置 不错
http://jingyan.baidu.com/article/22a299b51b83d39e19376aae.html //百度百科 安装 gnome
http://blog.chinaunix.net/uid-20769200-id-4373716.html //gnome、kde的安装和卸载