How to change Joomla - K2 - item via code?

Question

I tried this :

$row = JTable::getInstance('K2Item', 'Table');
$row->load($myId);
//change something
$row->title = 'New title';

$row->save(); // doesn't work
$row->checkin(); // doesn't work either

I was going also through most of the K2 code but it seems to rely on request variables and I have a hard time to understand that code at all.

Does anyone knows what's the right procedure?

thanks