You could change your current page from bean like this :
FacesContext.getCurrentInstance().getExternalContext().redirect("/accueil.jsf");
And for show message you can use :
FacesContext.getCurrentInstance().addMessage(null, new FacesMessage(FacesMessage.SEVERITY_WARN,"Sample warn message", "Watch out for PrimeFaces!"));
And add in your XHTML page :
<p:messages id="messages" showDetail="true" autoUpdate="true" closable="true" />