Not so often needed, be carefully with removing non existent IPv6 address, sometimes using older kernels it results in a crash.
Usage:
# /sbin/ip -6 addr del <ipv6address>/<prefixlength> dev <interface>
Example:
# /sbin/ip -6 addr del 3ffe:ffff:0:f101::1/64 dev eth0
# /sbin/ifconfig <interface> inet6 del <ipv6address>/<prefixlength>
# /sbin/ifconfig eth0 inet6 del 3ffe:ffff:0:f101::1/64