How to shrink the headers / chapters in dissertation?

I want to reduce the font size for headers (chapters). As you can see in the picture, the header is too big. Is there any command that will do the job?

My dissertation TeX file contains 1-chapters, 2-Main and 3-ref. All commands have been written in the Main file.

Following are the all packages which I use.

usepackage[T1,T5]{fontenc}

usepackage{colordvi,cite,comment,color}
usepackage{subfigure}

%usepackage{amsbsy,amsfonts,amsmath,amssymb,amsthm,amsxtra}

usepackage{epsfig,fancyhdr,latexsym}

usepackage[stable]{footmisc}

usepackage{amscd}

usepackage{amsfonts}

usepackage{indentfirst}

usepackage{verbatim}

usepackage{amsmath}

usepackage{showlabels}

usepackage{cite}

usepackage{hyperref}

usepackage{enumitem}

usepackage{cancel}

usepackage{todonotes}

usepackage{amssymb}

hypersetup{colorlinks=true, urlcolor=black}

hypersetup{citecolor=black}

usepackage[subfigure]{tocloft}

usepackage{sectsty}

allsectionsfont{normalsizeraggedright}

usepackage{sectsty}
allsectionsfont{normalsizeraggedright}