You'll need to create a bittrex account and send your bytes to your byte wallet address on there. Here's a link to bittrex: https://bittrex.com/

Then, exchange bytes for btc. After that, buy steem or sbd using the btc on blocktrades. Here's the link to there: https://blocktrades.us/

Bittrex requires you to have a minimum amount of btc to send, before they you'll be able to send it.