如何使用SharePoint 2010中的lists.asmx Web服务更新给定项目的内容类型？

I am building a XML then I feed the xml to lists.asmx web services (updatelistitems) method. It works great. Now I need to add additional field. for example I have a column called "CT" and it's populated with Content Type name that I need to assign. so if CT has a value "Sales" then I need to assign "Sales" content type. How to assign content type using lists.asmx call with updatelistitems method?I am building a XML then I feed the xml to list