Changing the index on existing field

Elastic Stack Elasticsearch
1

I have imported bunch of records from mySQL using the river plugin. Now I want to change the index of email and logonname field to not_analyzed

CURL -XPUT 'http://localhost:9200/dcio/users/_mappings' -d '
{
"users": {

        "properties" : {
            "logonName" : { "type" : "string", "index" : "not_analyzed" },
            "email" : { "type" : "string", "index" : "not_analyzed" }

        }
		
}

}'

I get an error following error

{
"error": "MergeMappingException[Merge failed with failures {[mapper [email] has different index values, mapper [email] has different tokenize values, mapper [email] has different index_analyzer, mapper [logonName] has different index values, mapper [logonName] has different tokenize values, mapper [logonName] has different index_analyzer]}]",
"status": 400
}

How can I change this index? I'm using 1.0 RC1