Not so often needed manually, mostly done by network configure scripts on shutdown (full or per interface)
Usage:
| # /sbin/ip -6 route del <ipv6network>/<prefixlength> via <ipv6address> ¬ [dev <device>] | 
Example:
| # /sbin/ip -6 route del default via 2001:0db8:0:f101::1 | 
Usage:
| # /sbin/route -A inet6 del <network>/<prefixlength> gw <ipv6address> [dev ¬ <device>] | 
Example for removing upper added route again:
| # /sbin/route -A inet6 del default gw 2001:0db8:0:f101::1 |