uploads.html

<form name="artist_basic_profile" id="artist_basic_profile" action="" method="post" enctype="multipart/form-data">
    <?php if($user->ID){ ?>
        <input type="file" id="userProfileImage" name="userProfileImage" >
        <input id="submit" type="submit" name="submit" value="Save" >
    <?php } ?>
</form>

uploads.php

require_once(ABSPATH . '/wp-load.php');
            require_once(ABSPATH . "wp-admin" . '/includes/file.php');
            require_once(ABSPATH . "wp-admin" . '/includes/image.php');

            $filename = $_FILES['userProfileImage']['name'];
            if($filename){
                $uploaddir = wp_upload_dir(); // get wordpress upload directory
                $myDirPath = $uploaddir['path'];
                $myDirUrl = $uploaddir['url'];

                $MyImage = rand(0, 5000) . $_FILES['userProfileImage']['name'];
                $image_path = $myDirPath . '/' . $MyImage;
                move_uploaded_file($_FILES['userProfileImage']['tmp_name'], $image_path);

                $file_array = array(
                    'name'     => $_FILES['userProfileImage']['name'],
                    'type'     => $_FILES['userProfileImage']['type'],
                    'tmp_name' => $_FILES['userProfileImage']['tmp_name'],
                    'error'    => $_FILES['userProfileImage']['error'],
                    'size'     => $_FILES['userProfileImage']['size'],
                );

                $file = $MyImage;
                $uploadfile = $myDirPath . '/' . basename($file);
                $filename = basename($uploadfile);
                $wp_filetype = wp_check_filetype(basename($filename), null);
                $attachment = array(
                    'post_mime_type' => $wp_filetype['type'],
                    'post_title'     => preg_replace('/\.[^.]+$/', '', $_FILES['userProfileImage']['name']),
                    'post_content'   => '',
                    'post_status'    => 'inherit'
                );
                $attachment_id = wp_insert_attachment($attachment, $uploadfile);
                $attach_data = wp_generate_attachment_metadata($attachment_id, $uploadfile);
                $attachimage_url = $uploaddir['url'] . '/' . basename($filename);
                wp_update_attachment_metadata($attachment_id, $attach_data);
                update_field('profile_image', $attachment_id, "user_" . $current_user_id);
            }