Always start with toolsbeta.
The current release of Kubernetes is 1.21. We aim to stay within the supported versions, and while there is currently a 1 year support cycle starting at 1.20, we are at 1.17. On those versions only three minor versions were supported for patches, so we've dropped clean off. We should try to move to 1.19 as soon as is feasible as well.
Make sure you read https://v1-18.docs.kubernetes.io/docs/setup/release/notes/#urgent-upgrade-notes
Then there's the appropriate upgrade guide: https://v1-18.docs.kubernetes.io/docs/tasks/administer-cluster/kubeadm/kubeadm-upgrade/
And then there's our notes: https://wikitech.wikimedia.org/wiki/Portal:Toolforge/Admin/Kubernetes/Upgrading_Kubernetes