在Linux中更换软件源，通常是编辑 /etc/apt/sources.list 文件或者在 /etc/apt/sources.list.d/ 目录下的相关.list文件。以下是更换为阿里云源的例子：

1.备份原有的 sources.list 文件：

sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup

2.编辑 sources.list 文件：

sudo nano /etc/apt/sources.list

3.将文件中的内容替换为阿里云源（以Ubuntu为例）：

deb http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse

4.保存文件并退出编辑器。

5.更新软件源：

sudo apt update

请根据您使用的Linux发行版和版本，从对应的软件源提供商那里获取正确的源地址。上述例子中的 bionic 是Ubuntu 18.04的代号，如果您使用的是其他版本，请替换为相应的代号，例如 focal 对应Ubuntu 20.04。