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In Ubuntu to install or remove a package there are several ways, here some:
From Ubuntu Software center, with is a graphic program and very easy and intuitive to use.
With Aptitude which is a program that runs in a terminal, although not as easy as the other one, or with pure commands in the terminal. Such as:
sudo aptitude install packagename
With apt-get which is a pure command line program to install or remove packages.
sudo apt-get install packagename
Those 3 programs when the machine is connected to the internet will automatically connect to the repositories of Ubuntu download and install the packages.
Or yet if you have the package already downloaded it is possible to use the program dpkg to install or remove a package.
sudo dpkg -i packagename
For more information about how to use aptitude, apt-get and dpkg, type in the terminal the following command:
That will open the manual for almost any program installed in your system.