LATAM doesn't upgrade on the counter... you should bid beforehand. With some few exceptions most flights will leave with full J cabins.. mix of paid and courtesy/bid upgrades. Depending on how full your flight is showing, 500 might work. In my experience on these flights there are usually 3-7 Black and Black Signature members that have priority above bids. So if the flight has less available seats than these there will be no bids accepted. Of course this is just my own experience and YMMV