Follow the steps for installing a plugin as they are described at http://pkp.sfu.ca/ojs/

It may be beneficial to create a tar.gz of this plugin and use the web tool for installing it.  
Otherwise, you will need to insert the correct reference into the versions table.

Alternatively, you may download a version of the plugin here:

http://etcdev.hil.unb.ca/jason/ocs-statisticsAggregator.tar.gz

It requires the latest version of OJS in order to function, and preferably a reasonably recent version
of PHP.