From the vCenter Web Client or ESXi Host UI it is not possible to expand the NFS datastore as this is a file level datastore. Hence ESXi hosts does not have privileges to expand the NFS datastore and we cannot see any option to expand the NFS datastore via the vCenter Web Client or the ESXi Host UI.
Engage your storage vendor/Admin to expand the datastore from the storage array.
Once it has been expanded, click refresh under the summary page of the datastore from vCenter to reflect the newly expanded size.