Assuming you already have your connection to the Access database and where:
OleDbConnection AccessCon = new OleDbConnection();
OleDbCommand cmd = default(OleDbCommand);
OleDbDataReader reader = default(OleDbDataReader);
string cmdUpdate = null;
Then something in the line of:
cmdUpdate = "UPDATE TABLE_NAME " + "SET COLUMN_j = '" + TextBox1.Text + "' " + "WHERE ID(ROW_i) = " + TextBox2.Text;
cmd = new OleDbCommand(cmdUpdate);
try {
cmd.Connection = AccessCon;
cmd.CommandType = CommandType.Text;
reader = cmd.ExecuteReader();
} catch (Exception ex) {
MessageBox.Show(ex.Message);
}
reader.Dispose();
PS: I'm not a star at C#, thus the above is converted from vb.net.