 
  
Hit up your MongoShell:
db.runCommand({
	$eval : db.COLLECTION_NAME.find({
		FIELD_NAME : {
			$exists : true,
			$type : 2
		}
	}).forEach( function(obj) {
		obj.FIELD_NAME = new NumberInt(obj.FIELD_NAME);
		db.COLLECTION_NAME.save(obj);
	}),
	nolock: true
});All types have a numeric identifier and a full list can be seen here.
Much quicker than processing type operators on the application side. However, large collections will lock the database so your mileage will vary!