Help->Install new software->Add->http://subclipse.tigris.org/update_1.6.x
If you are behind firewall you would get error like this
Unable to connect to repository http://subclipse.tigris.org/update_1.6.x/content.xml Unable to connect to repository http://subclipse.tigris.org/update_1.6.x/content.xml Connection refused
Then do the following,
- In Eclipse (go to Preferences > General > Network connections).
- Select "Active Provider" as "Manual".
- Select HTTP and click edit.
- Enter the host and port [proxy host and port get it from office admin]
- Select "Reuries Authentication" and enter the username and password.
Repeat Step 1 to 5 for Https.
Src: http://stackoverflow.com/questions/4598167/eclipse-updates-not-working