Q:

How to manage size of tkz points?

\documentclass{article}
\usepackage{pgfplots}
\usepackage{tkz-euclide}
\usetkzobj{all}
\begin{document}

\begin{tikzpicture}

\tkzInit[xmax=25,ymax=25]

\tkzDefPoint(0,0){C}

\tkzDefPoint(0,2){B}

\tkzDefPoint(0,4){A}

\tkzDefPoint(4,0){F}

\tkzDefPoint(4,2){E}

\tkzDefPoint(4,4){D}

\tkzDrawPoints[color=black,shape=circle,fill=black](C, B, A, D, E, F)

\tkzLabelPoint[left](C){$C$}

\tkzLabelPoint[left](B){$B$}

\tkzLabelPoint[left](A){$A$}

\tkzLabelPoint[right](D){$D$}

\tkzLabelPoint[right](E){$E$}

\tkzLabelPoint[right](F){$F$}

\tkzDrawSegments(A,D A,E A,F)
\tkzDrawSegments(B,D B,E B,F)
\tkzDrawSegments(C,D C,E C,F)
\end{tikzpicture}

\end{document}

Question:  How can i increase and decrese the size of tkz points?

A:

size=<number>, giving a size in points, or size=<length> (e.g. size=5mm). Add to the \tkzDrawPoints options.
\documentclass{article}
\usepackage{tkz-euclide}
\usetkzobj{all}
\begin{document}

\begin{tikzpicture}

\tkzInit[xmax=25,ymax=25]

\tkzDefPoint(0,0){C}
\tkzDefPoint(0,2){B}
\tkzDefPoint(0,4){A}
\tkzDefPoint(4,0){F}
\tkzDefPoint(4,2){E}
\tkzDefPoint(4,4){D}

\tkzDrawPoints[color=black,shape=circle,fill=black,size=15](C, B, A, D, E, F)

\tkzLabelPoints[left](A,B,C)
\tkzLabelPoints[right](D,E,F)

\tkzDrawSegments(A,D A,E A,F)
\tkzDrawSegments(B,D B,E B,F)
\tkzDrawSegments(C,D C,E C,F)
\end{tikzpicture}

\end{document}

