This software repository URL,
http://download.eclipse.org/eclipse/updates/4.3-M-builds/
, provides access to the software repository for the Eclipse Project.
This particular repository site is for Kepler (pre-release) Maintenance builds.
For more information about installing or updating software, see the Eclipse Platform Help.
There is also a collection of handy, downloadable all-in-one zip files available for many interests and platforms. Many people find these all-in-one packages the easiest way to get started.