I want to update or add Conversation dialog programmatically. is there any way to update or create dialog in Conversation service without editing manually.
There is no exposed API yet to automatically upload a JSON file to a workspace.
But you can certainly build your own JSON and manually upload.
Watson assistant now has a workspace API that allows you to programmatically build your own workspace. More details on the API page.
https://console.bluemix.net/apidocs/assistant#list-workspaces (See Workspaces -> Dialog Nodes).