Steem is on sale right now so it's a good time to power up. To transfer steem dollars into steem;
Top right of the page, 3 bar dropdown --> Currency Market --> Lower left under buy steem click Available --> fields should auto fill (if not refresh page and try again) --> Buy Steem
This will let you purchace Steem with your Steem Dollars. It will appear usually in moments in your wallet as Steem, which you can then power up.
To power up --> Wallet --> dropdown arrow next to Steem --> Power up
Doing all of this will increase your voting power fairly quickly :)