Are my hiking boots too big?

I can't advise you on the size to try, even though I have a pair of older (several generations back) Merrell Chameleons. I can report that they will stretch a bit over time, perhaps because of the generous ventilation panels.

However, for future reference, here's what I do when ordering boots or shoes online whenever I'm unfamiliar with the model and/or I can't find a pair in a local shop to try first: order more than 1 pair in order to try them first, then return the pairs that you least like. I've done this several times with boots, and most online shoe/boot stores aren't averse to doing it. Yeah, you have to pay for both pairs up front, and you have to pay for return shipping, but we're talking about the most important part of your anatomy for...ahem...walking. Still, by far the best method is to travel to where you can actually try the shoes or boots on with someone to help. REI is perfect for this. Any extra cost will more than repay itself in comfort.

 I bought a pair of those thinking they would be great for warm weather trail hiking. Really comfortable, light weight and seemingly well ventilated. After wearing them for a few day hikes an issue developed with not being able to get them to stay cinched down enough to prevent heel slip, their very nature of being a stretch shoe with a bungee type lacing system prevents them from staying just tight enough for me, particularly annoying was the left shoe, when my feet get just sweaty enough the heel slip causes what I can only describe as a farting noise at every single heel plant. Lesson learned stick with regular non stretch lace up footwear.