To my knowledge you cannot install .LRN from the APM. You need to:
- Stop your server.
- Drop your database
- Create it again
- Copy /var/lib/aolserver/yourservername/packages/dotlrn/install.xml to /var/lib/aolserver/yourservername
- Start your server again
When accessing your server now, you should see some notion about .LRN being installed.