只需在属性中更改目标框架即可:

在解决方案资源管理器中右键单击您的项目.
从下拉列表中选择属性"
在应用程序"选项卡中，选择目标框架"下拉列表.
选择您想要的版本.
保存属性，然后重新构建.

Just change the target framework in the properties:

Right click your project in the Solution Explorer.
Select "Properties" from the drop down
In the "Application" tab, select the "Target Framework" dropdown.
Pick the version you want.
Save the properties, and re-build.