you need to have the company struck off in the Companies Registration Office, until then the company will stlil have to file returns with the CRO.
you could do the strikeoff yourself, following details on the link above, much easier option though is to get a specialist co to do it for you, there are lots of good deals about at the moment just google coany strike off services, one i've used is. mystrikeoff.ie i am an accountant & the firm i work in use specialist companies for this all the time.