You can manage the App Engine Java and GWT Web Toolkit SDKs by opening Eclipse's workspace preferences, which can be accessed via Window > Preferences, or Eclipse > Preferences if you are on Mac OS X. Open the Google entry in the left pane and select Web Toolkit or App Engine.
You can click the Download button to open a web page where you'll find the latest SDKs.
Updating the App Engine Java SDK
When a new version of the App Engine Java SDK is available, the Google Plugin for Eclipse informs users via Eclipse update notifications.
Adding a new SDK is easy. If you click on the Add... button, you'll see the following:
Enter the path to the directory where the SDK is installed. If the location that you choose does not point to a valid SDK, an error message will be displayed.
To remove an SDK, select the SDK that you'd like to remove, and click the Remove button.
Note: If you remove the default workspace SDK and there are other SDKs available, a new default is chosen automatically.
Changing the Default SDK
To change the default SDK, click on the checkbox of the SDK that you'd like to use as the new default.
Caution: All projects in the workspace that use the default SDK will be rebuilt with the libraries from the newly-selected default SDK.
Selecting SDKs for a project
A project that uses GWT and/or App Engine always uses one of the SDKs that was installed into the workspace. To view or modify the project's SDK settings, right-click the project and select Google > Web Toolkit Settings... or Google > App Engine Settings....
Note: When you switch the project's SDK, that project's build path will be
updated to use the new SDK. If the project has a WAR directory that is used for launches
and deploys (configurable in project properties: Google > Web Application),
WEB-INF/lib folder will be updated with the new SDK libraries. Finally,
the project will be rebuilt, and the SDK will be