In AWS, EC2 by default provide 8GB space, in a past project I had to extend the size of one of my development instance as the data was growing fast. From AWS console add new EBS volume. Then attach it to your instance by AWS console and log into you EC2 instance via ssh.
Run following command:
sudo fdisk -l
which will show list of volumes with the newly added volume as unpartitioned. Something like below:
Then next step is to build the file system of new EBS volume using unix command mkfs. Like below:
sudo mkfs -t ext4 /dev/xvdf
Next you have to mount it in your desired path, e.g. /mnt/ebs1. Run following command:
sudo mount /dev/xvdf /mnt/ebs1
Then add an entry into /etc/fstab. it would be something like this:
"/dev/xvdf /mnt/ebs1 ext4 defaults 1 1"
There are facts if you add the EBS volume to your /etc/fstab and some how if there are issue (like file system corruption, unavailability of zone etc ) with the volume during booting the instance it will not be booted. Because while booting your system will look for the entry and when its not available the whole instance is down. Check AWS forum post for details.
And also check this whole SO discussion to resolve this issue in alternative way ( using a script for example).
Check following docs if you are more interested about the unix commands that used in this post.