PLEASE HELP ... (Probably a very quick reply only needed)

I'm new to photoshop & just learning the ropes, however on the following guide here : http://tricks.onigo.net/wiki/index.php?n=Main.FixRedEyeAndEnhanceEyes

Step 4 has a little proble, if you look at the 5th picture down, theirs a box thats meant to pop up that says "Levels" on it, i did a practise run at this once & it popped up, now I've follwed the instructions again & the box isn't popping up, where do i go please to show this box, it's frustrating me big time.

Thanks in advance to anyone who kindly helps me out here.

This is the box i can't get to appear up again :



I'm guessing it's probably something simple that i need to press, but I'm lost & can;t find it all for the last 20 mins or so :(

I'm not sure if it's the same with a MAC (if you're using one), but if you go to Image > Adjustments > Levels..., the Levels box will pop up.