https://msdn.microsoft.com/en-us/library/cc716697.aspx
In the Model Browser, right-click the .edmx file and select Update Model from Database.
The Update Model Wizard starts. If there is no database connection specified, the Choose Your Database Connection dialog box appears. Otherwise, the Choose Your Database Objects dialog box appears.
注意:
更新的时候，无法获取修改之后的字段类型。
变通的方法，就是删除掉，那个字段，然后重新Update