Reading Rel Note Chapter 4, update apt line. If (backport) packages conflict during upgrade, see 4.5.5 and force remove the packages. The last source.list will be as follows# cat sources.list # deb http://ftp.jp.debian.org/debian/ squeeze main deb-src http://ftp.jp.debian.org/debian/ squeeze main deb http://security.debian.org/ squeeze/updates main deb-src http://security.debian.org/ squeeze/updat