http://www.reliasoft.com/doe/

You have to pay the license for full version of Reliasoft design of experiment. I recommend you use alternative software like Minitab as it is much better than Reliasoft design of experiment in terms of analysis capability ...etc

Dear Prof Omar , thanks for your comment. I have the minitab but I do not know how to use it for the analysis . Can you be of assistance to me in explaining or sending materials that can help me use the software . I intend to use it for four factors with three replicate each

Hi Oluwafemi,

I can guide you in terms of applying RSM using Minitab Software by following few steps if you wish.

Regards 

I will appreciate sir

@ Omar, i am still waiting for the steps you promised to guide me with