>how to replace vfp native button with customized button ?

Place new one and delete old one (copying code first of course - and change tab orders,buttonname). If you mean how to do it hacking the scx (backup and do at your own risk):

use myForm.scx
replace class with 'myButtonClass', classloc with 'c:\myCLassLibPath\myClasslibName.vcx' ;
for lower(class) == 'commandbutton' and classloc==''
use
compile form myForm

PS:You could also change with aselobj() at designtime.
Cetin