Amazon AWS just released (on 13th February 2017) a new feature that allows to change a size of an EBS volume.
This allows to increase the size of an EBS volume on an existing instance, while it is running.
It is important to note that changing the volume size, does not change the size of the filesystem on the volume (for most filesystems). Additional steps might be required (depending on filesystem) in the operating system itself. For example a
ext4 filesystem used by most Linux OS today.
Full documentation from AWS describing the process can be found at http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-expand-volume.html
In some cases the block device has mapped partitions, and only then one (or more) of the partitions include a filesystem. In this case the partition will need to be resized first, and only then the filesystem. This process is described in the documentation as well.
The new "online" resize feature described in the blog only applies to current generation instances, and there are some other considerations and limitations that need to be checked before attempting a volume resize.