Original in Chinese, but it is useful for English speaking people to use, just try to translate with my own words and steps. Simple so far.
Step 1: Add IPv6 for VPN: on your Instnace page, click the VPC name, on the Action pull-down, select Edit CIDRs, just add IPv6.
Step 2: Add IPv6 CIDR for subnet: On the instance page again, click the subnet ID, there on Actions menu, Edit IPv6 CIDRs, input the required two digits as “00” for the first subnet, click Save.
Step 3: Add all the related IPv6 security group inbound rule, just copy all IPv4, but change the source as ::/0
Step 4: Assign IPv6 address to Instance: In the “Manage IP Addresses” window, just click assign on the IPv6, it will auto-assign the existing IPv6 address.
Step 5: Add IPv6 route table to the Internet Gateway, On the VPC page, click “Route Tables” menu, in the Actions, select Edit Routes, just add a new routes which destination is “::/0” and Target as “Internet Gateway” and then select the right Internet gateway.
Step 6: Use ping6 to verify new IPv6 address is pingable, and last step to goto your DNS provider add AAAA record for your domains.