When I stand up facing the speakers the sound is quite different as I have always been led to believe the left speaker is the main speaker for sound.
There are a few different things going on here so lets break it down to make sure I haven't misunderstood you.
Vincent is spot on, some powered speaker have the build-in stereo amp in one speaker and the other is passive, and connected by a wire. This doesn't make one a "main speaker for sound", they both should give out as much sound.
Vincent is also correct if you swap your RCA inputs you will make your left speaker the right and so on.
However, is that really what you really want to do? In the original post you said:
but when we sit with our back to the speakers they are not giving out the right signal. the powered speaker which should be the left speaker is the right so I want to turn them around
Are you suggesting that they sound OK when you face them, but not so good when you face away?
That is normal, our ears are shaped forward, and we normally face our loudspeakers so you have trained your brain to perceive a soundstage that way. Some people who listen to a lot of music on a system with a good sound stage experience a phenomenon when listening to headphones, that the music is coming from behind them.
Making left right, and right left isn't going to fix the issue, and it will make it even worse when you turn around. If you mainly listen to music with your back to the speakers, try playing with the positioning of the speakers. If you have the toe in, maybe reduce that a little, if they are not to in, try and introduce a little of that maybe with a crossover point in front of you when your back is to the system.