here u have to use appdelegate class object of tabbarcontroller to chage index or tab
try following
[self.tabBarController setSelectedViewController:<#(UIViewController *)#>];
or
[self.tabBarController setSelectedIndex:<#(NSUInteger)#>];
for example
app_appAppDelegate *appdelegate=(app_appAppDelegate *)[[UIApplication sharedApplication]delegate];
[appdelegate.tabBarController setSelectedIndex:2];
i have get the rough code may give error so please check it
EDIT
app_appAppDelegate *appdelegate=(app_appAppDelegate *)[[UIApplication sharedApplication]delegate];
[appdelegate.tabBarController setSelectedViewController:[appdelegate.tabBarController.viewControllers objectAtindex:1]];