I have followed the steps for resizing an EC2 volume
login into AWS web console -> EBS -> right mouse click on the one you wish to resize -> "Modify Volume" -> change "Size" field and click [Modify] button
growpart /dev/xvda 1
resize2fs /dev/xvda1
This is a cut-to-the-chase version of Dmitry Shevkoplyas' answer. AWS documentation does not show the growpart command. This works ok for ubuntu AMI.