There really is a tutorial for everything online. Here's a video from Howcast showing guys who don't want to seem like they've got no experience how to undo their special lady friend's bra with one hand.

It basically outlines 3 things you need: 1. Willing partner. 2. Location of clasp. 3. A free warm hand.

It also tells you the difference between normal bras and sports bras just so you don't ever get confused.

So yeah, don't panic.

And finally, it teaches you how to release the clasp.

Watch the video below: