Cannot implicitly convert type string to byte

How to solve the problem ?

Error 1 Cannot implicitly convert type 'string' to 'byte' 

  OleDbCommand cmd = new OleDbCommand("select r1,r2,r3,r4 from ope", Con);
            Con.Open();
            OleDbDataReader dr = cmd.ExecuteReader();
            if (dr.Read())
            {
                y[0] = dr[0];
                y[1] = dr[1];
                y[2] = dr[2];
                y[3] = dr[3];
            }
            dr.Close();
            Con.Close();
            y[x] += 1;
            OleDbCommand cmd2 = new OleDbCommand("update ope set r" + Convert.ToString(x + 1) + " = " + Convert.ToString(y[x]), Con);
            int updated = 0;
            Con.Open();
            updated = cmd2.ExecuteNonQuery();
            Con.Close();
            Panel1.Visible = false;
            Panelxxx.Visible = true;