This can be configured per Ingress resource using the nginx.ingress.kubernetes.io/proxy-body-size annotation.

For example:

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  annotations:
    nginx.ingress.kubernetes.io/proxy-body-size: 150m
    certmanager.k8s.io/acme-challenge-type: dns01
    certmanager.k8s.io/acme-dns01-provider: azuredns
    certmanager.k8s.io/cluster-issuer: letsencrypt-production
    kubernetes.io/ingress.class: nginx