Nevermind. I've figured out a good way. For all of you who are trying to do this, simply go to NuGet Package Manager. Search for "Metro Framework Installer". Install it.
Then go to Project > Add Reference, go to your project folder and add the MetroFramework.dll and MetroFramerwork.Design.dll as references.
Then go to your form and change the base class (form) to MetroFramework.Forms.MetroForm