Existing is the easier of the two. It requires little effort, strife, or work to exist,
just take nourishment at regular intervals, breath in and out as required, perform hygienic functions, etc.
Living: Take all 'just' above and add in fighting for what is good and right, do your personal best everyday, laugh/cry, lose/win, love/hate. To live is to experience life, not just to pass through it unaffected.