-Once AMCAS is submitted, it is closed. You cant submit updated grades thru that. The AMCAS GPA is the one that schools will use
-You can submit updated grades to schools. However, not all schools accept updates; these updated grades will not be part of any recalculated GPA (AMCAS will be used); and if you application is already "complete" with primary, secondary, MCAT and LOR, it will already be in evaluation and the updates may not be seen except in passing at a review meeting