I downloaded some sounds and would like to use them in a commercial game, but i dont know, if do i can chop and convert the sounds into smaller parts? for example there are engine sounds but i only need a portion of that sound that is loopable for car engine..
Yes, that's the whole point of the sampling+ license. Please read http://freesound.iua.upf.edu/legal.php
As long as you obey the conditions set out in the license, it should be fine. Remember to attribute the samples!