An exorcism is a sacramental, not a sacrament, for the care of souls, even souls not of the flock. The following document from the US Conference of Catholic Bishops outlines what it is and how it is to be executed.
Note 1: Before a priest does an exorcism, he goes to confession.
Note 2: American exorcists have reported a dramatic increase in numbers in the last few years.
Note 3: Following is a list of well-known Catholic exorcists from the past and present. I can add one more: Father Gary Thomas, SF Bay Area. Go to an authorized Catholic priest.