How to change enumerate item from 1. to (1)?

Here's a solution that doesn't require loading a separate package (such as enumerate or enumitem): Just issue the command

\renewcommand\labelenumi{(\theenumi)}

in a TeX group, before \begin{enumerate}. (To make the scope of \renewcommand\labelenumi{(\theenumi)} global, place the instruction in the preamble.)

Here's the output of an MWE that also shows how one may cross-reference enumerated items:

\documentclass{article}
\begin{document}

\begingroup
\renewcommand\labelenumi{(\theenumi)}
\begin{enumerate}
\item A first item.  \label{item:1}
\item A second item. \label{item:2}
\end{enumerate}
\endgroup
\noindent
Here are some cross-references to items \ref{item:1} and \ref{item:2}.

\end{document}

Finally I found what I was looking for

\usepackage{enumerate}

\begin{enumerate}[{(1)}]
\item 
.
.
.
\end{enumerate}