How to set the height of a window using c#?

This is how I would do it:

using System;
using System.Diagnostics;
using System.Runtime.InteropServices;

namespace ConsoleApplication1
{
    class Program
    {
        [StructLayout(LayoutKind.Sequential)]
        public struct RECT
        {
            public int left;
            public int top;
            public int right;
            public int bottom;
        }

        [DllImport("user32.dll", SetLastError = true)]
        static extern bool GetWindowRect(IntPtr hWnd, ref RECT Rect);

        [DllImport("user32.dll", SetLastError = true)]
        static extern bool MoveWindow(IntPtr hWnd, int X, int Y, int Width, int Height, bool Repaint);

        static void Main(string[] args)
        {
            Process[] processes = Process.GetProcessesByName("notepad");
            foreach (Process p in processes)
            {
                IntPtr handle = p.MainWindowHandle;
                RECT Rect = new RECT();
                if (GetWindowRect(handle, ref Rect))
                    MoveWindow(handle, Rect.left, Rect.right, Rect.right-Rect.left, Rect.bottom-Rect.top + 50, true);
            }
        }
    }
}

While you can do it with SetWindowPos, and SetWindowPos is the newer and more capable API, MoveWindow is just easier to call.