Refer the code.

protected void txtamount_TextChanged(object sender, EventArgs e)
{
    CalculateTotal();
}

protected void gvtrans_RowDeleting(object sender, GridViewDeleteEventArgs e)
{
    string index = gvtrans.DataKeys[e.RowIndex].Values[0].ToString();
    DataTable dt = ViewState["CurrentTable"] as DataTable;
    for (int i = 0; i < dt.Rows.Count; i++)
    {
        if (dt.Rows[i]["RowNumber"].ToString() == index)
        {
            dt.Rows.Remove(dt.Rows[i]);
            ViewState["CurrentTable"] = dt;
        }
    }
    gvtrans.DataSource = dt;
    gvtrans.DataBind();
    SetPreviousData();
    CalculateTotal();
}

private void CalculateTotal()
{
    decimal total = 0;
    foreach (GridViewRow row in gvtrans.Rows)
    {
        TextBox Debits = row.FindControl("txtamount") as TextBox;
        total += Convert.ToDecimal(Debits.Text == "" ? "0" : Debits.Text);
    }
    Session["DebitTotal"] = total;
    (gvtrans.FooterRow.FindControl("lblTotal") as Label).Text = total.ToString();
    txtrecamt.Text = (gvtrans.FooterRow.FindControl("lblTotal") as Label).Text;
}