If you are comfortable using the Terminal, you can use apt (Advanced Packaging Tool) to install or remove software. You need administrative access to use apt.

To update the local list of packages, enter in a Terminal:

apt-get update

To install all available updates:

apt-get upgrade

To install a package:

apt-get install package

To remove a package:

apt-get remove package

To list other apt commands and options:

apt-get help

For more information, see Debian’s apt manual.