You don't get free upgrades by right on BAEC as a silver or gold, though if you get to 2500 tier points you get an upgrade voucher for one trip for two, and at 3500 two upgrade vouchers for one.
You MAY get complimentary upgrades depending on loading and BA's algorithm for selecting people for schmoozing. Don't bank on it though.
As a gold you can often upgrade using avios on your own booked tickets, which is relatively good value.