Downloaded to Mac OSX 10.9 Tried to install on my website

Downloaded to Mac OSX 10.9

Tried to install on my website Wordpress plug in
Got this message

Installing Plugin from uploaded file: 296442_wpmu-dev-dashboard-3.4.1.zip
Unpacking the package…

Installing the plugin…

Destination folder already exists. Cinetpub/vhosts/basingstokehypnotherapy.org/httpdocs/wp-content/plugins/wpmudev-updates/

Plugin install failed.

Whats the way to open this up and download plugins?

Thanks
David