Using \usepackage{enumitem} will allow you to customize the enumerate environment label.

• \arabic* for 1, 2, 3…
• \alph* for a, b, c…
• \Alph* for A, B, C…
• \roman* for i, ii, iii…
• \Roman* for I, II, III…

For example, the following code:

\begin{enumerate}[label=(\arabic*)]
    \item first item
    \item second item
\end{enumerate}

will produce

Circled label will be a bit trickier:

\begin{enumerate}[label=\large\protect\textcircled{\small\arabic*}]
    \item First item
    \item Second item
    \item Third item
    \item Fourth item
\end{enumerate}

    \textcircled{\small{2}}

or

    {\large \textcircled{\small 2}}

or

    {\Large \textcircled{\normalsize 2}}                  

will produce