adjusting the kernel of a Gaussian filter

Im trying to Create a normalized Gaussian filter to blur an image. I need to make the filter 256x256 pixels, with a kernel of 4x4. The problem is that I can't find a function that lets me adjust the kernel. What I have right now:

H=fspecial('gaussian',256,4);

x=imfilter(XnoisyBlur,H);

figure(3)

imshow(x)

H1=(abs(H));

F=(x).*(1./H).*((H1.^2)/((H1.^2)+200));

figure(4)

imshow(F)

To create a gaussian and then deconvolve it. The deconvolved image always turns up black, and I think my gaussian is the issue.