无法下载 Ubuntu 16.04 的更新

我想通过软件更新程序将我的笔记本电脑从 Ubuntu 15.10 升级到 16.04 并遇到以下问题。

错误消息如下。

Failed to fetch http://ubuntu.uhost.hk/pool/universe/p/pidgin/libpurple0_2.10.11-0ubuntu5_amd64.deb 404  Not Found
Failed to fetch http://ubuntu.uhost.hk/pool/universe/libg/libgtk2-perl/libgtk2-perl_1.2498-1_amd64.deb 404  Not Found
Failed to fetch http://ubuntu.uhost.hk/pool/universe/libp/libpango-perl/libpango-perl_1.227-1_amd64.deb 404  Not Found
Failed to fetch http://ubuntu.uhost.hk/pool/universe/r/rhythmbox/rhythmbox-plugin-cdrecorder_3.3-1ubuntu4_amd64.deb 404  Not Found
Failed to fetch http://ubuntu.uhost.hk/pool/universe/r/rhythmbox/rhythmbox-plugin-magnatune_3.3-1ubuntu4_amd64.deb 404  Not Found
Failed to fetch http://ubuntu.uhost.hk/pool/universe/e/empathy/account-plugin-jabber_3.12.11-0ubuntu1_amd64.deb 403  Forbidden
Failed to fetch http://ubuntu.uhost.hk/pool/universe/e/empathy/account-plugin-yahoo_3.12.11-0ubuntu1_amd64.deb 403  Forbidden
Failed to fetch http://ubuntu.uhost.hk/pool/universe/e/empathy/account-plugin-salut_3.12.11-0ubuntu1_amd64.deb 403  Forbidden
Failed to fetch http://ubuntu.uhost.hk/pool/universe/e/empathy/mcp-account-manager-uoa_3.12.11-0ubuntu1_amd64.deb 403  Forbidden
Failed to fetch http://ubuntu.uhost.hk/pool/universe/e/empathy/account-plugin-aim_3.12.11-0ubuntu1_amd64.deb 403  Forbidden
Failed to fetch http://ubuntu.uhost.hk/pool/universe/e/empathy/empathy_3.12.11-0ubuntu1_amd64.deb 403  Forbidden
Failed to fetch http://ubuntu.uhost.hk/pool/universe/e/empathy/empathy-common_3.12.11-0ubuntu1_all.deb 403  Forbidden
Failed to fetch http://ubuntu.uhost.hk/pool/universe/t/telepathy-gabble/telepathy-gabble_0.18.3-2_amd64.deb 404  Not Found
Failed to fetch http://ubuntu.uhost.hk/pool/universe/t/telepathy-mission-control-5/telepathy-mission-control-5_5.16.3-1ubuntu6_amd64.deb 404  Not Found
Failed to fetch http://ubuntu.uhost.hk/pool/universe/t/telepathy-mission-control-5/libmission-control-plugins0_5.16.3-1ubuntu6_amd64.deb 404  Not Found
Failed to fetch http://ubuntu.uhost.hk/pool/universe/t/telepathy-salut/telepathy-salut_0.8.1-5_amd64.deb 404  Not Found
Failed to fetch http://ubuntu.uhost.hk/pool/universe/t/telepathy-logger/telepathy-logger_0.8.2-1_amd64.deb 404  Not Found
Failed to fetch http://ubuntu.uhost.hk/pool/universe/t/telepathy-logger/libtelepathy-logger3_0.8.2-1_amd64.deb 404  Not Found
Failed to fetch http://ubuntu.uhost.hk/pool/universe/b/brasero/brasero-cdrkit_3.12.1-1ubuntu2_amd64.deb 403  Forbidden
Failed to fetch http://ubuntu.uhost.hk/pool/universe/b/brasero/brasero_3.12.1-1ubuntu2_amd64.deb 403  Forbidden
Failed to fetch http://ubuntu.uhost.hk/pool/universe/libk/libkate/libkate1_0.4.1-7_amd64.deb 404  Not Found
Failed to fetch http://ubuntu.uhost.hk/pool/universe/u/ubuntu-sso-client/ubuntu-sso-client-qt_13.10-0ubuntu11_all.deb 404  Not Found
Failed to fetch http://ubuntu.uhost.hk/pool/universe/u/ubuntu-sso-client/ubuntu-sso-client_13.10-0ubuntu11_all.deb 404  Not Found
Failed to fetch http://ubuntu.uhost.hk/pool/universe/u/ubuntu-sso-client/python-ubuntu-sso-client_13.10-0ubuntu11_all.deb 404  Not Found
Failed to fetch http://ubuntu.uhost.hk/pool/universe/p/puredata/puredata-core_0.46.7-3_amd64.deb 404  Not Found
Failed to fetch http://ubuntu.uhost.hk/pool/universe/g/gavl/libgavl1_1.4.0-4_amd64.deb 404  Not Found
Failed to fetch http://ubuntu.uhost.hk/pool/universe/g/gnome-icon-theme/gnome-icon-theme_3.12.0-1ubuntu2_all.deb 403  Forbidden
Failed to fetch http://ubuntu.uhost.hk/pool/main/t/talloc/libtalloc2_2.1.5-1ubuntu1_amd64.deb 404  Not Found
Failed to fetch http://ubuntu.uhost.hk/pool/universe/p/pidgin/libpurple-bin_2.10.11-0ubuntu5_all.deb 404  Not Found
Failed to fetch http://ubuntu.uhost.hk/pool/universe/libv/libvisual-plugins/libvisual-0.4-plugins_0.4.0+dfsg1-8_amd64.deb 403  Forbidden
Failed to fetch http://ubuntu.uhost.hk/pool/main/t/talloc/python-talloc_2.1.5-1ubuntu1_amd64.deb 404  Not Found
Failed to fetch http://ubuntu.uhost.hk/pool/universe/s/software-center/software-center_16.01+16.04.20160217_all.deb 404  Not Found

如何解决？