using System.Text;
using System.Web.Security;
using System.Security.Cryptography;

public static string HashPassword(string plainMessage)
{
byte[] data = Encoding.UTF8.GetBytes(plainMessage);
using (HashAlgorithm sha = new SHA256Managed())
{
byte[] encryptedBytes = sha.TransformFinalBlock(data, 0, data.Length);
return Convert.ToBase64String(sha.Hash);
}
}

private MembershipPasswordFormat passwordFormat;
passwordFormat = MembershipPasswordFormat.Hashed;

if (passwordFormat == MembershipPasswordFormat.Hashed)
{
string newPassword = "Type your new pwd here"
txtpswd.Text = HashPassword(newPassword);
}