My Nav 300 looks like it has an adjustable stem(I think that what it's called) where the top half can me moved forward and down. I'd like to do this to give me a more leaned forward ride. But the bike has a sticker on it saying not to adjust the stem because the bolts have been properly tightened. I'm wondering if it in fact can be adjusted to different positions or if it's a two piece stem that can't be adjusted. I think I remember someone else saying they had adjusted their's. Looking for input, thanks.