You can sell your voting power on smartsteem.com it will not effect on your steempower. Or you can delegate your steempower to smartsteem.com only. Delegation is like renting your steempower you can take it back too. And if you upvote on some other post you will get some curation rewards.
For delegating your sps there is one more site known as minnowbooster.net.
For vote selling I will suggest you smartsteem.com because I'm too using and it is giving better profit