In order to download and install ADT you will first need to configure an Eclipse remote update, this can achieved via the following steps:
1. Start Eclipse, then select Help > Software Updates > Find and Install….
2. In the dialog that appears, select Search for new features to install and press Next.
3. Press New Remote Site.
4. In the resulting dialog box, enter a name for the remote site (e.g. Android Plugin) and enter this as its URL: https://dl-ssl.google.com/android/eclipse/.
5. Press OK.
6. You should now see the new site added to the search list (and checked).
7. Press Finish.
8. In the subsequent Search Results dialog box, select the checkbox for Android Plugin > Eclipse Integration > Android Development Tools and press Next.
9. Read the license agreement and then select Accept terms of the license agreement, if appropriate.
10. Press Next.
11. Press Finish.
12. The ADT plugin is not signed; you can accept the installation anyway by pressing Install All.
13. Restart Eclipse.
14. After restart, update your Eclipse preferences to point to the SDK root directory ($SDK_ROOT):
Select Window > Preferences… to open the Preferences panel. (Mac OS X: Eclipse > Preferences)
Select Android from the left panel.
For the SDK Location in the main panel, press Browse… and find the SDK root directory.
15. Press Apply, then OK
Updating the ADT Plugin
To update the ADT plugin to the latest version, follow these steps:
1. Select Help > Software Updates > Find and Install….
2. Select Search for updates of the currently installed features and press Finish.
3. If any update for ADT is available, select and install.
1. Select Help > Software Updates > Manage Configuration.
2. Navigate down the tree and select Android Development Tools
3. Select Scan for Updates under Available Tasks.