here is change password code for simple match old password and enter new password

Change password in php

<?php

if(isset($_POST['update_psss'])){
                  $oldpassword = $_POST['oldpassword'];
                  $newpassword = $_POST['newpassword'];
                  $confirmnewpassword = $_POST['confirmnewpassword'];

                  if ($oldpassword==$oldpassworddb){


                  if (strlen($newpassword)>25||strlen($confirmnewpassword)<6)   
                  {
                  echo "Password must be betwwen 6 & 25";
                  }else{


                  if($newpassword==$confirmnewpassword){
                  $sql="UPDATE users SET password='$newpassword' where  id='$login_id'";

                 $result = mysqli_query($connection, $sql);

                  if($result){

                    header('Location: logout.php?success=1');

                  }

         } else
                  {
                 echo "Passwords do not match";
                 }
       }
     }else{
       echo "old password not matched";
     }
              }


?>