Tente algo assim (supondo que você esteja usando o Linux):
#Define parameters
INSTANCE=i-abcd1234
ASG_NAME="current-autoscaling-group-name"
OLD_LC="old-launch-configuration-name"
NEW_LC="new-launch-configuration-name"
# Create AMI
IMAGE='aws ec2 create-image --instance-id $INSTANCE --name NEW-IMAGE --output text'
# Create Launch Configuration
aws autoscaling create-launch-configuration --launch-configuration-name $NEW_LC --image-id $IMAGE --instance-type t2.micro
# Update Auto Scaling Group to use new Launch Configuration
aws autoscaling update-auto-scaling-group --auto-scaling-group-name $ASG_NAME --launch-configuration-name $NEW_LC
# Delete old Auto Scaling Group
aws autoscaling delete-launch-configuration --launch-configuration-name $OLD_LC