Helm is a package manager for Kubernetes that provides a declarative and versioned approach to application deployment and lifecycle management. When updating configuration values for an existing Helm release, the recommended and best-practice approach is to use helm upgrade, optionally with the --set flag or a values file, to apply the new configuration while preserving the release's history.

Option A is correct because helm upgrade updates an existing release in a controlled and auditable manner. Helm stores each revision of a release, allowing teams to inspect past configurations and roll back to a previous known-good state if needed. Using --set enables quick overrides of individual values, while using -f values.yaml supports more complex or repeatable configurations. This approach aligns with GitOps and infrastructure-as-code principles, ensuring consistency and traceability.

Option B is incorrect because modifying Helm-managed resources directly with kubectl edit breaks Helm's state tracking. Helm maintains a record of the desired state for each release, and manual edits can cause configuration drift, making future upgrades unpredictable or unsafe. Kubernetes documentation and Helm guidance strongly discourage modifying Helm-managed resources outside of Helm itself.

Option C is incorrect because deleting and reinstalling a release discards the release history and may cause unnecessary downtime or data loss, especially for stateful applications. Helm's upgrade mechanism is specifically designed to avoid this disruption while still applying configuration changes safely.

Option D is also incorrect because editing chart source files directly and reapplying them bypasses Helm's release management model. While chart changes are appropriate during development, applying them directly to a running release without helm upgrade undermines versioning, rollback, and repeatability.

According to Helm documentation, helm upgrade is the standard and supported method for modifying deployed applications. It ensures controlled updates, preserves operational history, and enables safe rollbacks, making option A the correct and fully verified best practice.