How to update Eclipse from 2018-09 to 2018-12

See Eclipse FAQ - Always enable major upgrades:

To always enable major upgrades of your IDE once and for all:

1. from the Available Software Sites preference page
2. enable the Latest Eclipse release http://download.eclipse.org/releases/latest repository by ticking the checkbox.
3. Apply and Close
4. Check for updates

The similar workflow can be used to hide and disable automatic proposal of major upgrades.

To my knowledge, the update site http://download.eclipse.org/releases/latest exists since Eclipse Photon (4.8) in Window > Preferences: Install/Update > Available Software Sites but is not checked by default.

If you want to change the default of this preference, vote for or comment on Eclipse bug 539281 - Enable http://download.eclipse.org/releases/latest by default.

The two advantages of using the Eclipse Installer over the direct installation of one or more IDE packages are:

• The Eclipse Installer saves disk space when installing multiple IDE packages (by using a shared pool for the plug-ins of all IDE packages)
• The Eclipse Installer makes it easier to contribute to an Eclipse project (advanced mode).