Unable to change field type using API

I am unable to change the type of a field using the API.

I am using the PUT endpoint on PUT /xearch/_schema/{table_name}/{field_name} replaceXearchField() - Update field type from string to integer as follows:

{
  "label":  "Test 5",
  "type":  "integer"
}

The error message that I am receiving is

Screen Shot 2016-11-02 at 4.03.19 PM.png914x203 38.8 KB