Add plugin to Bitnami WP stack

I run Bitnami WP 3.5 stack (on Ubuntu). I can’t figure out how to make plugin addition word from the dashboard. I can add them manually with scp, but much of wpmudev functionality is missing without this capability.

The FTP is running ok, but after a while the system says that the (wp-content) directory is not found. This is a rights issue, but what gives?

Appreciate a tip, if anyone knows what to do!