To increase the disk space of your server, there are 2 options.
1) Create a snapshot of the server by pressing the cogwheel in the server list and the selection "Create snapshot" (Figure 1).
Figure 1. Create a snapshot
2) Navigate to the Snapshot section from the menu and list your snapshots.
3) Press the cogwheel of your newly created snapshot and hit "Launch instance" (Figure 2).
Figure 2. Launch instance
You will be able to choose all basic informations, RAM, Volume size, etc.
1) Follow this guide to start running commands against the OpenStack native API and then run the following API commands;
2) List the VMs you want to resize and save the UUID of the server you want to resize
openstack server list
3) List possible flavors to use: (pick one with the intended new disk size).
openstack flavor list
4) Resize to a new flavor:
openstack server resize --flavor <flavor-uuid> <server-uuid>
When the resize completes, the instance status will be VERIFY_RESIZE. You can now confirm the resize to change the status to ACTIVE.
5) Confirm the resize:
openstack server resize confirm <server-uuid>