First off, that isn't VB, or VB.NET. It's C#...
Secondly, don't use ToString and string comparison:
private void Form1_KeyUp(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Left)
pictureBox1.Location = new Point(pictureBox1.Location.X - 20, pictureBox1.Location.Y);
else if (e.KeyCode == Keys.Right)
pictureBox1.Location = new Point(pictureBox1.Location.X + 20, pictureBox1.Location.Y);
else if (e.KeyCode == Keys.Up)
pictureBox1.Location = new Point(pictureBox1.Location.X, pictureBox1.Location.Y - 20);
else if (e.KeyCode == Keys.Down)
pictureBox1.Location = new Point(pictureBox1.Location.X, pictureBox1.Location.Y + 20);
}
Third, the form probably won't get the KeyUp event anyway: If there is any control on your form which can take keyboard input, it will get the focus, and will get the keys instead (since it is supposed to handle keys, and the form isn't) - so will will need to handle this in the various controls, rather than at the form.
Fourth, it is more normal to handle KeyDown, or KeyPress, rather than KeyUp anyway...