i have installed pidgin but its old version
i saw at freshports latest version 2.5.2 so i wanted install from fresh ports. . .
pidgin-2.5.2 is in ports. To install, do as ale said:
# cd /usr/ports/net-im/pidgin && make install clean

If it is not in your ports tree, you need to update (again, as ale told you before :p )
If you have it installed, remove it before rebuilding it or read the paragraphs about updating with portupgrade/portmaster/portmanager in the same page I've linked before.