Often times, there are two sets of settings for picture size.

One resides in the television itself.
The other resides in the cable/sat/DVR box.

You might consider turning your television to 16.9 settings, and then changing the input on the cable box. Some boxes allow you to easily find the menu system to change the picture size, others can be difficult and require a call to the cable/sat service provider to walk you through.

Keep me posted.