\usepackage{titlesec}
% Customize chapter style
\titleformat
{\chapter} % command
[hang] % shape
{\bfseries\normalsize\centering} % format
{Chapter\ \thechapter:} % label
{1pt} % sep
{
} % before-code
[
] % after-code

\titleformat
{\section} % command
[hang] % shape
{\bfseries\normalsize\centering} % format
{\thesection.} % label
{1pt} % sep
{
} % before-code
[
] % after-code

\titleformat
{\subsection} % command
[hang] % shape
{\bfseries\normalsize\centering\itshape} % format
{\thesubsection} % label
{1pt} % sep
{
} % before-code
[
] % after-code


