How can I delete the Time Machine backup files on a Netgear ReadyNAS?
In Finder, click Go => Connect To Server...
In the Server Address field, type "afp://xxx.xxx.xxx.xxx" (IP address) or "afp://your-ngnas-name.local"
Connect using the credentials you use to connect to the Time Machine service.
Finder will open a window in /Volumes/ReadyNAS. You should see a list Time Machine's .sparsebundle files.


At this point, you can delete a .sparsebundle. It's also possible to Ctrl+Click on a .sparsebundle and select "Show Package Contents" to browse inside.

UPDATE Sometimes files inside the sparsebundle package or the package itself will be locked, preventing deletion. To unlock: Get Info > General > Locked > uncheck.