How to update a UI label from a non UI thread in iOS

I am new to iOS development, I have plain objective -c class "MoneyTimer.m" for running timer, from there i want to update the an UI label with the changing value of timer. I want to Know how to access the UI element from non UI thread ? I am Using Xcode 4.2 and storyboarding.

In blackberry simply by getting the event lock one can update the UI's from non UI thread.

//this the code from MyTimerClass

 {...
    if(nsTimerUp == nil){

        nsTimerUp = [NSTimer scheduledTimerWithTimeInterval: 1.0 target:self selector:@selector(countUpH) userInfo:nil repeats: YES];
 ...}

(void) countUpH {

sumUp = sumUp + rateInSecH;
 **//from here i want to update the UI label **
...
}