How do I update iPhone IOS without doing anything else?

OK, let me begin by letting you know I am a bit of a technophobe. I have had my iPhone 4 for 2 years now and never plugged it into a laptop apart from when I bought it to set it up. Its getting a little slow now so could do with an update I think. So, I have 2 questions...

1) When I plug it into a laptop, will it give me a choice of IOS? At the moment I guess its got version 4 or something, I know 6 is out, but I'm worried about the stupid apple maps thing. So, do I get a choice and if so, should I choose 6? Or 5?

2) Do I need to set something in itunes or maybe on the phone to stop it doing some sort of auto update of music (and apps?) and wiping everything?

Thank you, and apologies for being a bit of a phone idiot. It would be excusable if I was 75, but I'm 31 and should know better!