To change the target .NET Framework version or profile
In Visual Studio, open the project you want to change.
Right-click the project in Solution Explorer and then click Properties.
In the Project Designer, locate the Target Framework list, as follows.
For Visual Basic projects, click the Compile tab and then click Advanced Compile Options. The Target Framework list is in the Advanced Compiler Settings dialog box.
For Visual C# projects, the Target Framework list is on the Application tab of the Project Designer. For more information, see Application Page, Project Designer (C#).
For Visual F# projects, the Target Framework list is on the Application tab of the Project Designer.
In the Target Framework list, select the .NET Framework version or profile that you want.
When you click OK, the project unloads and then reloads in the integrated development environment (IDE). The project now targets the .NET Framework version that you just selected.