Just to echo some of the comments. It is best to try and provide as much information as possible. The class you using is a Springer-Verlag class and can be downloaded here.
You can add the following in your preamble:
\makeatletter
\long\def\@makecaption#1#2{%
\captionstyle
\ifx\@captype\fig@type
\vskip\figcapgap
\fi
\setbox\@tempboxa\hbox{{\floatlegendstyle #1\floatcounterend}%
\capstrut #2}%
\ifdim \wd\@tempboxa >\hsize
{\floatlegendstyle #1\floatcounterend}\capstrut #2\par
\else
\hfill\unhbox\@tempboxa\hfill\hfill%
\fi
\ifx\@captype\fig@type\else
\vskip\tabcapgap
\fi}
\makeatother
Use the template.tex test file that comes with the bundle to test. Testing it with the above I got:

When you inserting your figures or tables, use the \centering command to ensure that the figure or tabular is also centered:
\begin{figure}
\centering
\image....
\caption...
\end{figure}
To be honest, it will look awful with small figures or tables and will probably break the \sidecaption command that is provided by the class. It is also possible the Journal Editor will not be very happy for you to change the look and feel.
\documentclass[smallextended,natbib]{svjour3}. – Grzenio Mar 2 '12 at 18:28svjour3.clsisn't on ctan or tex live, so i can't easily look at it. however, in that file, if it follows the pattern ofarticle.cls, there may be a definition for a command\@makecaption. inarticleand similar classes, the caption text is stored in a box, and the box measured. if the width is less than the allowable caption width, it will be centered; otherwise it is set as a paragraph.svjour3.clsmay do things differently, but that is where you need to look. – barbara beeton Mar 2 '12 at 20:19