Package managers that you use on a debian based distro
Debain distros use dpkg.
To install a package for firefox browser which has been downloaded at /root/firefox.deb. The dependencies might fail.
$ sudo dpkg -i /root/firefox.deb
To install a package using APT
$ sudo apt install firefox
Lets now locate the package to install Chromium browser in the system. Use apt search functionality to locate the correct package name. The browser has the description of: Chromium web browser, open-source version of Chrome
$ sudo apt search chromium-browser
To install the chromium-browser
sudo apt install -y chromium-browser
To remove the firefox browser from the system.
$ sudo apt remove firefox