To change/modify the existing records in a database table, we have to use UPDATE statement.

Syntax:

UPDATE table_name SET column1=value, column2=value2,... WHERE column_name=some_value

Consider our table has the following records:

MySQLi Procedural

<?php
/* Attempt MySQL server connection. Assuming you are running MySQL
server with default setting (user 'root' with no password) */
$link = mysqli_connect("localhost", "root", "", "demo");
 
// Check connection
if($link === false){
    die("ERROR: Could not connect. " . mysqli_connect_error());
}
 
// Attempt update query execution
$sql = "UPDATE persons SET email='peterparker_new@mail.com' WHERE id=1";
if(mysqli_query($link, $sql)){
    echo "Records were updated successfully.";
} else {
    echo "ERROR: Could not able to execute $sql. " . mysqli_error($link);
}
 
// Close connection
mysqli_close($link);
?>

MySQLi Object Oriented

<?php
/* Attempt MySQL server connection. Assuming you are running MySQL
server with default setting (user 'root' with no password) */
$mysqli = new mysqli("localhost", "root", "", "demo");
 
// Check connection
if($mysqli === false){
    die("ERROR: Could not connect. " . $mysqli->connect_error);
}
 
// Attempt update query execution
$sql = "UPDATE persons SET email='peterparker_new@mail.com' WHERE id=1";
if($mysqli->query($sql) === true){
    echo "Records were updated successfully.";
} else{
    echo "ERROR: Could not able to execute $sql. " . $mysqli->error;
}
 
// Close connection
$mysqli->close();
?>

PDO 

<?php
/* Attempt MySQL server connection. Assuming you are running MySQL
server with default setting (user 'root' with no password) */
try{
    $pdo = new PDO("mysql:host=localhost;dbname=demo", "root", "");
    // Set the PDO error mode to exception
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch(PDOException $e){
    die("ERROR: Could not connect. " . $e->getMessage());
}
 
// Attempt update query execution
try{
    $sql = "UPDATE persons SET email='peterparker_new@mail.com' WHERE id=1";    
    $pdo->exec($sql);
    echo "Records were updated successfully.";
} catch(PDOException $e){
    die("ERROR: Could not able to execute $sql. " . $e->getMessage());
}
 
// Close connection
unset($pdo);
?>

In the above example PHP code will update the email address of a person in the persons table whose id equals to 1. After executing the code the persons table will look like this: