Consider the publication by Rudolf Zeller in Ref. [1]. One performs two self-consistent calculations, one spin-polarised calculation, and one spin-non-polarised one. One subsequently calculates the magnetisation M according to Eq. (18) in Ref. [1]. The Stoner (exchange) parameter I can now be determined by solving the second equality in Eq. (19) in a least-squares sense for the relevant bands (the ones close to the chemical potential). One can also determine I by solving the second equality in Eq. (20), namely

(a) n±(ε) = n0(ε ± Ι Μ/2),

where n±(ε) and n0(ε) are calculated according to the first equality in Eq. (20) of Ref. [1]; the former is determined in terms of ε±kν, and the latter in terms of ε0kν.

Lastly, calculation of the Stoner parameter requires calculation of the transverse magnetic susceptibility. The many-body theory underlying this calculation is described in Ref. [2]. The considerations in this reference are focussed on a lattice model, however one can along the same line, and rather straightforwardly, deduce the formalism relevant to a continuum model. 

[1] R Zeller, Spin-Polarized DFT Calculations and Magnetism, in Computational Nanoscience: Do It Yourself!, editd by J Grotendorst, S Blügel, and D Marx (NIC Series, Jülich, 2006).

http://juser.fz-juelich.de/record/54009/files/FZJ-2014-02225.pdf

[2] M Fleck, AM Oleś, and L Hedin, Phys. Rev. B 56, 3159 (1997).

http://juser.fz-juelich.de/record/54009/files/FZJ-2014-02225.pdf

Thanks for your answer. Your answer seems to me a rather technical which I already know. What I want to know is how practically I can determine the Stoner Exchange parameter by using any DFT software package. I want to know the steps, not the mathematics...

You are welcome Suman.

I think I explained how the calculations are done, or can be done, by explicitly referring you to the expressions underlying the relevant calculations. Whatever DFT software you may be using, it should be capable of calculating for instance the total density of electronic states, for both spin-polarised and spin-compensated ground states. How a software package is to be made to output the Stoner parameter, I do not know. Perhaps you should emphasise this point in your question (naming also the software package that you have in mind) so as to draw the attention of  the people who have the necessary technical expertise.

Yes 99% of the DFT softwares gives the total density of states. After obtaining the total density of states, what steps should I follow next???Is the quantity M is the total magnetic moment of the whole structure of the magnetic moment per unit cell??

All details are described in the paper by Rudolf Zeller, which I have cited. Please consult it. Please also consult my first response on this page.