To enable NAT function, you must DISABLE Source/Destination Check to let this happen.
https://forums.aws.amazon.com/message.jspa?messageID=340550
Stop the Instance
Detach the original volume from the instance
Create a snapshot of the original volume(old instance)
Create a new volume from the snapshot, specifying a larger size(As per requirement)
Attach the new volume to the instance
Start the instance and find its old public IP
Login on the server
sudo resize2fs /dev/sda1