Hi,

There are many different types of "hiss"  if you are talking about something that sounds like tape hiss, you should be able to get rid of most of it using EQ but it will affect the quality and frequency response on the vocals.  Far better to find the source of the hiss (it could be your mic, a preamp if you are using one, your mixer, a unshielded microphone cable or one where the shield has become disconnect or broken)  and these are just a few of the causes.  Find the source of the problem and you will not need to worry about getting rid of it in post.  Low cost audio hardware and cables produce most of the problems associated with hiss. 

The post production alternative is to use a product such as audacity or magix has a product called audio cleaning lab.  Download the free trial and see if it solves your problem.  The magix product you will eventually have to purchase.  Audacity is a free product but requires that you really understand audio post production and editing.

Good Luck,

George