This guide walks through replacing a running Ubuntu installation on an OVH VPS with a fresh Arch Linux base system, using OVH's built-in Rescue Mode as the installation environment. No external ISO (not available for VPS) or boot image (again, arch it's not available for VPS) is used.
WARNING: This process will completely wipe your existing VPS disk. Back up all data, databases, configuration files, and SSH keys before proceeding.