How do I decrease or increase the size of these points in tikz?

Question

\documentclass{article} 
\usepackage{import}
\usepackage[dvipsnames]{xcolor}
\usepackage{tikz}
\usepackage{pgfplots}
\usetikzlibrary{calc}

\begin{document}

\begin{figure}[h]
\centering
    \begin{tikzpicture}
\begin{axis}[name=plot,
width=0.75\textwidth,
height=\axisdefaultheight,
xmin=250, xmax=750,
ymin=0, ymax=0.7,
minor tick num=1,
ytick distance=0.20,
xlabel={$\lambda \, \mathrm{(nm)}$},
ylabel={$\mathrm{Abs}$},
every axis plot/.append style={ultra thick},
legend pos={north east}]
\addplot[RoyalBlue] table[x index=0,y index=1]{c8.txt};
\addplot[Blue, mark=*] coordinates {(619, 0.1716)} node[anchor=south]{$\lambda = 617,\!5$};
\addplot[Blue, mark=*] coordinates {(259.5, 0.6228)} node[anchor=west]{$\lambda = 259,\!5$};
\end{axis}
    \end{tikzpicture}
\caption{Espetro de abroção da fração 8 da primeira cromatografia}
\label{pupu}
\end{figure}

\end{document}

Answer 1

\documentclass[tikz, border=1cm]{standalone} 
\usepackage{pgfplots}
\pgfplotsset{compat=1.18}
\begin{document}
\begin{tikzpicture}
\begin{axis}[
xmin=250, xmax=750,
ymin=0, ymax=0.7,
minor tick num=1,
ytick distance=0.20,
xlabel={$\lambda \, \mathrm{(nm)}$},
ylabel={$\mathrm{Abs}$},
]
\addplot[blue, mark=*, mark size=1pt] coordinates {(619, 0.1716)} node[above]{$\lambda=617,5$};
\addplot[blue, mark=*, mark size=2pt] coordinates {(259.5, 0.6228)} node[right]{$\lambda=259,5$};
\end{axis}
\end{tikzpicture}
\end{document}