A DMR-EX83 isn't a Blu-ray player. In fact it doesn't have anything to do with Blu-ray at all. It is a DVD Recorder with a hard drive. So it plays DVDS (not Blu-ray discs) and it records to its internal hard drive or to blank DVD recordable discs.
What it does have is HD Upscaling. This takes standard definition images (the Freeview tuner, its own recordings and movies played off DVD) and upscales them to 1080p. That could be the source of your problem.
First things first, when playing DVDs in 4:3 format it's the TV and not the player that is used to change the picture shape. Look up Aspect Ratio in your TV manual, or you can find the Aspect Ratio switching button on the TV remote control. Try this by tuning in to a non-HD channel from Freeview and then use the button to change the picture shape.
The above should only work for Standard Definition (SD) channels and for unscaled SD sources. If you turn off the HD upscaling on the DMR-EX83 and let the TV do the scaling instead then you'll regain the ability to use the Aspect Ratio button on the TV when viewing DVDs and home recordings.
If your player really is a Blu-ray player then it won't be a DMR-EX83. Whatever the model I'm afraid you're stuck with 4:3 with black bars left and right. 1080i and 1080p signals are fixed to 16:9 format. Anything 4:3 is pillar boxed inside the 16:9 frame. That means bars left and right.