If you press "help" in the remote you get the Guide. In there there are some sections explaining various things. In some of them you can select the online version (which should be the most updated). It isn't really much but it's a start.
Still all you need for starting is the "Action menu". There you can set the picture and sound values while watching a video. There are various modes available for picture. Change between them and you should find one that fits best with your taste. Once selected you can then modify each single parameter. For what each one does you may check this video:
It's a general tutorial, but the parameters are about the same for all TVs.
Regarding the bad audio the answer is simple: buy a soundbar. Or even better a 5.1+ channels amplifier.
