Upload the files on your website root folder (like public_html or httpdocs)
version < 2.2.0 Edit the index.php, find the
$cache = new Cache('file');
and change it to
$cache = new Cache('apcu');
version >= 2.2.0
Edit the /system/config/default.php, find
$_['cache_type'] = 'file'; // apc, file or mem
$_['cache_expire'] = 3600;
change it to
$_['cache_type'] = 'apcu'; // apc, file or mem
$_['cache_expire'] = 3600;