You can do this in two ways:
- You download EMF as a set of eclispe plugins (i.e. JAR files), and you put them under the plugins/ or dropins/ directory from your Eclipse root directory
- (EASIEST WAY) From Eclipse, Help -> Install new software -> [here you select an update site from which you can install the EMF plugins]
Here you find the update site for EMF: http://www.eclipse.org/modeling/emf/updates/
You may also want to look at the EMF Installation wiki page: http://wiki.eclipse.org/EMF/Installation