Download the appropriate FCChat zip file:

FCChat for Joomla 1.5

FCChat for Joomla 1.6

FCChat for Joomla 1.7

FCChat for Joomla 2.5

Next, go to your Joomla administration area Extensions > Install/Uninstall.

In the Upload Package File section click Browse and locate FCChat zip file. Then click Upload File & Install to upload the file and complete the installation.

Procede to the next step, Activating the chat.