How to decrypt a string

Hello everyone I have a function that encrypts the password using sha1, and makes it perfect, what I do not know now how to decrypt it, someone could help me, this is my code to encrypt:

  public static string EncryptPassWord(string passwd)
    {
        byte[] temp;           
        SHA1 sha = new SHA1CryptoServiceProvider();
        temp = sha.ComputeHash(Encoding.UTF8.GetBytes(passwd));
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < temp.Length; i++)
        {
            sb.Append(temp[i].ToString("x2"));
        }
        return sb.ToString();
    }

for the string="test" returns me a94a8fe5ccb19ba61c4c0873d391e987982fbbd3 I would like it when I send that long string back to me "test".