How can I edit a Deployment without modify the file manually?

Question

You could do it via the REST API using the PATCH verb. However, an easier way is to use kubectl patch. The following command updates your app's tag:

kubectl patch deployment myapp-deployment -p \
  '{"spec":{"template":{"spec":{"containers":[{"name":"myapp","image":"172.20.34.206:5000/myapp:img:3.0"}]}}}}'

According to the documentation, YAML format should be accepted as well. See Kubernetes issue #458 though (and in particular this comment) which may hint at a problem.

There is a set image command which may be useful in simple cases

Update existing container image(s) of resources. Possible resources include (case insensitive): pod (po), replicationcontroller (rc), deployment (deploy), daemonset (ds), job, replicaset (rs)

kubectl set image (-f FILENAME | TYPE NAME) CONTAINER_NAME_1=CONTAINER_IMAGE_1 ... CONTAINER_NAME_N=CONTAINER_IMAGE_N

http://kubernetes.io/docs/user-guide/kubectl/kubectl_set_image/

$ kubectl set image deployment/nginx-deployment nginx=nginx:1.9.1
deployment "nginx-deployment" image updated

http://kubernetes.io/docs/user-guide/deployments/

(I would have posted this as a comment if I had enough reputation)

Yes, as per http://kubernetes.io/docs/user-guide/kubectl/kubectl_patch/ both JSON and YAML formats are accepted.

But I see that all the examples there are using JSON format. Filed https://github.com/kubernetes/kubernetes.github.io/issues/458 to add a YAML format example.

I have recently built a tool to automate deployment updates when new images are available, it works with Kubernetes and Helm:

https://github.com/rusenask/keel

You only have to label your deployments with Keel policy like keel.sh/policy=major to enable major version updates, more info in the readme. Works similarly with Helm, no additional CLI/UI required.