You can change global path thickness as below, so you no need to change it here and there:

\documentclass[tikz]{standalone}
\begin{document}

\tikzstyle{every node}=[font=\large]
\tikzstyle{every path}=[line width=2pt]

\begin{tikzpicture}[
   every node/.append style={circle, draw=blue!80, inner sep=2pt, minimum size=12pt}]
\node                 (1) at (0,0) {1};
\node[]               (2) at (1,0) {2};
\node[]               (3) at (2,0) {3};
\end{tikzpicture}
\end{document}

Output (use inkscape tool to covert pdf to png)

Output (use convert tool to covert pdf to png)

You can change global path thickness as below, so you no need to change it here and there:

\documentclass[tikz]{standalone}
\begin{document}

\tikzstyle{every node}=[font=\large]
\tikzstyle{every path}=[line width=2pt]

\begin{tikzpicture}[
   every node/.append style={circle, draw=blue!80, inner sep=2pt, minimum size=12pt}]
\node                 (1) at (0,0) {1};
\node[]               (2) at (1,0) {2};
\node[]               (3) at (2,0) {3};
\end{tikzpicture}
\end{document}

Output (use inkscape tool to covert pdf to png)

Output (use convert tool to covert pdf to png)

You can change global path thickness as below, so you no need to change it here and there:

\documentclass[tikz]{standalone}
\begin{document}

\tikzstyle{every node}=[font=\large]
\tikzstyle{every path}=[line width=2pt]

\begin{tikzpicture}[
   every node/.append style={circle, draw=blue!80, inner sep=2pt, minimum size=12pt}]
\node                 (1) at (0,0) {1};
\node[]               (2) at (1,0) {2};
\node[]               (3) at (2,0) {3};
\end{tikzpicture}
\end{document}

Output

You can change global path thickness as below, so you no need to change it here and there:

\documentclass[tikz]{standalone}
\begin{document}

\tikzstyle{every node}=[font=\large]
\tikzstyle{every path}=[line width=2pt]

\begin{tikzpicture}[
   every node/.append style={circle, draw=blue!80, inner sep=2pt, minimum size=12pt}]
\node                 (1) at (0,0) {1};
\node[]               (2) at (1,0) {2};
\node[]               (3) at (2,0) {3};
\end{tikzpicture}
\end{document}

Output (use inkscape tool to covert pdf to png)

Output (use convert tool to covert pdf to png)