solution is
you could get
 SecurityContext instance via SecurityContextHolder
 then via
 SecurityContext's setAuthentication(Authentication authentication)  
 UsernamePasswordAuthenticationToken is subclass of Authentication 
 so,you have to create a new one which contains new aurhorites(roles) via constructor as below shown

 SecurityContext 's setAuthentication. (UsernamePasswordAuthenticationToken(Object principal, Object credentials, GrantedAuthority[] authorities) ) ;



reference url:http://forum.springsource.org/showthread.php?52229-How-to-change-GrantedAuthority-dynamically