yii2:upload is faild for file larger than 2 mb

Question

i used kartik\file\FileInput for upload my file

my file is correct uploaded for file smaller than 2 mb !

what is my problem ????

echo '<label class="control-label">اضافه کردن فایل</label>';
    echo FileInput::widget([
        'model' => $model,
        'pluginOptions' => [
            'initialPreview' => [
                "../../$url",
            ],
            'initialPreviewAsData' => true,
            'initialCaption' => "",
            'initialPreviewConfig' => [
            ],
        ],
        'attribute' => 'file',
        'options' => ['multiple' => false,
            'accept' => "$acc/*",

        ]
    ]);
    }

this is my model :

class PostContent extends \yii\db\ActiveRecord
    {

    public $file;