Updating ROS package

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If you mean version update to a new debian package, you can just simply use apt, like; sudo apt-get install ros-indigo-costmap-2d . This will install the package if it is not installed, or upgrade it if it is installed and an upgrade is available. Of course before this operations it will be better to update repositories with sudo apt-get update.

For only upgrade (no install if it is not installed), you can use sudo apt-get --only-upgrade install ros-indigo-costmap-2d .

If you installed it from source, you should update your files according to the version control system used. For example if it is a git repository, and you installed it with git clone, you can just use git pull, or git fetch and merge.

Hope I got your point.