apt-get update

apt-get upgrade

cp /etc/apt/sources.list /etc/apt/sources.list.lenny

sed 's/lenny/squeeze/g' /etc/apt/sources.list > /etc/apt/sources.list.squeeze

cp /etc/apt/sources.list.squeeze /etc/apt/sources.list

apt-get update

apt-get dist-upgrade

Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages will be REMOVED:
  libept0 libxcb-xlib0
The following NEW packages will be installed:
  apt-xapian-index ca-certificates dash diffutils dmsetup firmware-linux-free gcc-4.4-base geoip-database gnupg-curl grub-pc insserv install-info isc-dhcp-client isc-dhcp-common iso-codes libbind9-60 libboost-iostreams1.42.0 libbsd0 libc-bin libcurl3-gnutls libdb4.7 libdb4.8 libdns69 libept1 libevent-1.4-2 libexpat1 libfile-copy-recursive-perl libfreetype6 libgeoip1 libgpgme11 libgssapi-krb5-2 libisc62 libisccc60 libisccfg62 libk5crypto3 libkrb5-3 libkrb5support0 liblwres60 liblzma2 libnfnetlink0 libpth20 libreadline6 libsasl2-modules libtokyocabinet8 libudev0 libuuid-perl libxapian22 linux-base linux-image-2.6.32-5-amd64 lsb-release os-prober python-apt python-apt-common python-chardet python-debian python-reportbug python-support python-xapian python2.6 python2.6-minimal sensible-utils xz-utils
The following packages will be upgraded:
  acpi-support-base acpid adduser apt apt-utils aptitude at base-files base-passwd bash bash-completion bc bind9-host bsd-mailx bsdmainutils bsdutils busybox console-common console-data console-tools coreutils cpio cron dc debconf debconf-i18n debian-archive-keyring debian-faq debianutils dhcp3-client dhcp3-common dictionaries-common diff dmidecode dnsutils doc-debian dpkg e2fslibs e2fsprogs ed eject file findutils ftp gcc-4.3-base gettext-base gnupg gpgv grep groff-base grub grub-common gzip hostname iamerican ibritish ifupdown info initramfs-tools initscripts installation-report iproute iptables iputils-ping ispell klibc-utils laptop-detect less libacl1 libattr1 libblkid1 libbz2-1.0 libc6 libc6-i386 libcap2 libcomerr2 libconsole libcwidget3 libdb4.6 libdevmapper1.02.1 libedit2 libgc1c2 libgcc1 libgcrypt11 libgdbm3 libgnutls26 libgpg-error0 libgpm2 libgssglue1 libidn11 libkeyutils1 libklibc libkrb53 libldap-2.4-2 liblocale-gettext-perl liblockfile1 libmagic1 libncurses5 libncursesw5 libnewt0.52 libnfsidmap2 libpam-modules libpam-runtime libpam0g libpci3 libpcre3 libpopt0 libreadline5 librpcsecgss3 libsasl2-2 libselinux1 libsepol1 libsigc++-2.0-0c2a libslang2 libsqlite3-0 libss2 libssl0.9.8 libstdc++6 libtasn1-3 libtext-charwidth-perl libtext-iconv-perl libtext-wrapi18n-perl libusb-0.1-4 libuuid1 libwrap0 libx11-6 libx11-data libxau6 libxcb1 libxdmcp6 libxext6 libxml2 libxmuu1 linux-image-2.6-amd64 locales lockfile-progs login logrotate lsb-base lsof m4 makedev man-db manpages mawk mime-support mktemp mlocate module-init-tools mount mutt ncurses-base ncurses-bin ncurses-term net-tools netbase nfs-common ntpdate openbsd-inetd openssh-client openssh-server openssl openssl-blacklist passwd patch pciutils perl perl-base perl-modules portmap postfix procmail procps python python-central python-minimal python2.5 python2.5-minimal readline-common reportbug rsyslog sed ssh ssl-cert sysv-rc sysvinit sysvinit-utils tar tasksel tasksel-data tcpd texinfo time traceroute tzdata ucf udev update-inetd usbutils util-linux vim vim-common vim-runtime vim-tiny w3m wamerican wget whiptail whois x11-common xauth zlib1g
212 upgraded, 62 newly installed, 2 to remove and 0 not upgraded.
Need to get 157MB of archives.
After this operation, 186MB of additional disk space will be used.
Do you want to continue [Y/n]? Y

...
Restarting services possibly affected by the upgrade:
  cron: stopping...starting...done.
  atd: stopping...starting...done.
...

reboot