Hello Anupam,
As Warren has mentioned one way to fix your issue is by attaching the root disk to another working instance and deleting the files. However, you need to delete your instance before attaching the root disk to another working instance. I would recommend taking a snapshot of your disk before deleting your instance to be on the safe side. Also, if you want to keep the same IP when creating the new instance make sure to reserve that IP as static before deleting the instance.
Another way to fix this issue would be by creating a bigger disk from the snapshot of current disk and creating a new instance with that disk as a root disk.
I hope that helps.
Faizan