You can access it two ways.
- Clicking on the link in your Daily Activites
- Going to the Arcade and scrolling down to Wheel of Wow
The Wheel will also change approximately every 2 weeks, if WW has maintenance usually there will be a new wheel with lots of great items to win.
If you haven't spun your wheel for the day and you do it during the "Hourly Event" instead of leaving the wheel by clicking ok on your prize just click spin again and it will spin the second time for you. If you win an Extra WOW Spin coupon just click the coupon in the bottom left and it will spin again.