kubectl config unset takes a dot-delimited path. You can delete cluster/context/user entries by name. E.g.

kubectl config unset users.gke_project_zone_name
kubectl config unset contexts.aws_cluster1-kubernetes
kubectl config unset clusters.foobar-baz

Side note, if you teardown your cluster using cluster/kube-down.sh (or gcloud if you use Container Engine), it will delete the associated kubeconfig entries. There is also a planned kubectl configrework for a future release to make the commands more intuitive/usable/consistent.

For clusters and contexts you can also do

kubectl config delete-cluster my-cluster
kubectl config delete-context my-cluster-context

There's nothing specific for users though, so you still have to do

kubectl config unset users.my-cluster-admin

Run command below to get all contexts you have:

$ kubectl config get-contexts
CURRENT   NAME             CLUSTER     AUTHINFO                                NAMESPACE
*         Cluster_Name_1   Cluster_1   clusterUser_resource-group_Cluster_1

Delete context:

$ kubectl config delete-context Cluster_Name_1

与问题无关，但可能是一个有用的资源。
看一看kubectx + kubens: Power tools for kubectl。
它们使切换上下文和命名空间变得很容易+可以选择删除

更改上下文：

kubectx dev-cluster-01

更改名称空间：

kubens dev-ns-01

删除上下文：

kubectx -d my-context