Please find inline replies for your questions:
You would need to follow the instructions described here for increasing the size of your instance's disk volume. Once the volume resizing is completed, you can reboot the instance and the disk partition will be automatically expanded to adapt to the new disk size.
Yes, there will be an increase according to the EBS costs, please see AWS' EBS pricing page for more details.
You can follow the instructions described here.
You can modify any file in the server accessing through SSH, please find the instructions here. You can also download/upload files using SFTP.
There are no plans to drop support for TestLink from the Bitnami Catalog. We only use to do it for solutions which have been abandoned by the upstream maintainers for a long time.
We can only provide support for issues caused by misconfigurations in the Bitnami TestLink Stack using these forums. For deeper application-related questions, we would recommend posting them in the official support channels from the TestLink project.