I'm not personally sure that anyone can these days. I know that all things are possible with Christ. But I put little stock in individual power to cast out demons, mainly because most Christians aren't focused enough on where the Power comes from; instead, they're more tempted to give themselves credit for any such miracle. I know the Bible tells us that the disciples did cast out demons (at least Paul did; some of the disciples simply said the demons were "subject to them; I'm not sure if they actually cast out demons, or if they were just saying they believed the demons were subject unto them); and most certainly Jesus did cast out demons, and most certainly He still can!
At any rate, the power to cast out evil spirits is obtained only through the name of Jesus.
Below is a link I found that explains it pretty well. Other than that, I say praying to Jesus asking Him to cast out evil spirits is the way to do it.