How do I use iTween in Update function in unity 5?

I have to rotate few objects around a capsule shaped track and have to manage the speeds at the run time as its a betting game and for that I am using iTween but its not running in update function so please can u make me clear?

If u know about that how can use iTween in update function to update the speed at the run time then please help me out as I am stuck here.

Thanks..!!!