Increasing the size of a PersistentVolumeClaim on GKE

I've heard that in later versions of Kubernetes (1.9 onwards if I'm not mistaken; I have 1.10), it's possible to expand a PersistentVolume as long as allowVolumeExpansion: true is set in the StorageClass configuration.

In my case, on GCP, the StorageClass my PVC uses does not have that line, and I cannot add it either.

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  annotations:
    storageclass.beta.kubernetes.io/is-default-class: "true"
  creationTimestamp: 2018-05-30T17:07:33Z
  labels:
    addonmanager.kubernetes.io/mode: EnsureExists
    kubernetes.io/cluster-service: "true"
  name: standard
  resourceVersion: "8741704"
  selfLink: /apis/storage.k8s.io/v1/storageclasses/standard
  uid: f1bd0421-642b-11e8-bb11-42010a9a00b5
parameters:
  type: pd-standard
provisioner: kubernetes.io/gce-pd
reclaimPolicy: Delete
volumeBindingMode: Immediate

So, I want to increase a PV, and its corresponding PVC from 8Gi to 100Gi. What's the best way of doing this? Is there a way to do it while preserving data, or must the current PV be deleted before making a new one?

Here's the PV YAML:

apiVersion: v1
kind: PersistentVolume
metadata:
  annotations:
    kubernetes.io/createdby: gce-pd-dynamic-provisioner
    pv.kubernetes.io/bound-by-controller: "yes"
    pv.kubernetes.io/provisioned-by: kubernetes.io/gce-pd
  creationTimestamp: 2018-05-31T10:30:39Z
  finalizers:
  - kubernetes.io/pv-protection
  labels:
    failure-domain.beta.kubernetes.io/region: europe-west2
    failure-domain.beta.kubernetes.io/zone: europe-west2-c
  name: pvc-a70ca000-64bd-11e8-bb11-42010a9a00b5
  resourceVersion: "8728415"
  selfLink: /api/v1/persistentvolumes/pvc-a70ca000-64bd-11e8-bb11-42010a9a00b5
  uid: a9e8c071-64bd-11e8-bb11-42010a9a00b5
spec:
  accessModes:
  - ReadWriteOnce
  capacity:
    storage: 8Gi
  claimRef:
    apiVersion: v1
    kind: PersistentVolumeClaim
    name: production-postgres
    namespace: neserver-6540663
    resourceVersion: "85487"
    uid: a70ca000-64bd-11e8-bb11-42010a9a00b5
  gcePersistentDisk:
    fsType: ext4
    pdName: gke-cluster-1-320626e3-pvc-a70ca000-64bd-11e8-bb11-42010a9a00b5
  persistentVolumeReclaimPolicy: Delete
  storageClassName: standard
status:
  phase: Bound