You can use a multiband dynamics compressor or get one of the many desser plugins available for free or otherwise.
FWIW, my usual go-to desser is the Digitalfishphones "Spitfish" http://www.digitalfishphones.com/main.php?item=2&subItem=5
Addendum: BTW, the Digitalfishphones suite is freeware.
I'll second the free Spitfish VST suggestion. I was having trouble with essing because of a cheap condenser mic. Used Spitfish and was able to really improve the vocals by a lot. And it's really easy to use.