Increase the disk space of C on the computer

We have a dedicated server on Hetzner with a website on Docker (+ Laravel framework) Contact with the developers has been lost Need to: - restore and change server access (probably SSH) - recommend a storage location and set up a full server backup with easy recovery, probably not on Hetzner for security - fix the logo that is not displaying for some reason (it's unclear why the file has become inaccessible) Important - there is no website backup, and there is no room for error. We will only consider experienced specialists.