The length of the string exceeds the value set on the maxJsonLength property

I send a request to Server and take a long response, seem like:

“Object”: “{“PDF”:“File content in encode base 64”}”

With a large file, I get the error in response:

“Message”: “Error during serialization or deserialization using the JSON JavaScriptSerializer. The length of the string exceeds the value set on the maxJsonLength property.”,>
“StackTrace”: " at System.Web.Script.Serialization.JavaScriptSerializer.Serialize(Object obj, StringBuilder output, SerializationFormat serializationFormat)\r\n at System.Web.Script.Serialization.JavaScriptSerializer.Serialize(Object obj, SerializationFormat serializationFormat)\r\n at System.Web.Script.Services.RestHandler.InvokeMethod(HttpContext context, WebServiceMethodData methodData, IDictionary`2 rawParams)\r\n at System.Web.Script.Services.RestHandler.ExecuteWebServiceCall(HttpContext context, WebServiceMethodData methodData)",

“ExceptionType”: “System.InvalidOperationException”

}

So, how can I increase maxJsonLength of response? Please help.
Thank very much