Not so often needed to use by hand, configuration scripts will use such on shutdown.
# /sbin/ip -6 route del <ipv6network>/<prefixlength> dev <device> |
# /sbin/ip -6 route del 2000::/3 dev eth0 |
# /sbin/route -A inet6 del <network>/<prefixlength> dev <device> |
# /sbin/route -A inet6 del 2000::/3 dev eth0 |