sudo apt update
sudo apt upgrade -y
sudo apt dist-upgrade -y
安装更新管理器核心包

sudo apt install update-manager-core -y
编辑 /etc/update-manager/release-upgrades 文件，将 Prompt 设置为 lts

sudo nano /etc/update-manager/release-upgrades
找到以下行并修改：

Prompt=lts
开始升级过程

sudo do-release-upgrade

　　可能会出现 ：

Please install all available updates for your release before upgrading.

输入：
do-release-upgrade
出现如下提示：
Please install all available updates for your release before upgrading.
方案1
通过手动方式安装更新：
sudo apt update
sudo apt upgrade
sudo apt dist-upgrade
sudo do-release-upgrade
这样就可以安装成功。
-----------------------------------------------------
如果以上方式不成功 

方案2
执行以下命令
cd /etc/apt/sources.list.d
for i in *.list; do mv ${i} ${i}.disabled; done
apt clean
apt autoclean
sudo do-release-upgrade
这样就可以安装成功。
-----------------------------------------------------
如果以上方式不成功 

方案3
执行以下命令
apt clean
apt autoclean
sudo apt update
sudo apt upgrade -y
sudo apt dist-upgrade

-----------------------------------------------------
如果以上方式不成功 

没有方案4