To convert Steem/SBD is not that difficult
First, simply login to your Steemit wall. Then, click on your wallet and click on the Cryptocurrency you desire to convert into.
After doing this, simply and choose "buy"
Let's say you have 10 steem and 40SBD and you intend getting Steem Power with steem. All you need to do is to go to your Steemit wallet and click on your steem. Then, you choose the 'buy'option, and you will be directed to block trade website where you can indicate the number of SBD you wish to convert to steem.
Very simple!