Don't want my iPhone 6s Plus anymore?

I bought an iPhone 6s Plus in december and I'm not able to adjust the size, I don't really like it anymore and I would love to switch to an iPhone 6s. However, I don't know if I can do that. How much would I have to pay? Any chance I could just switch it out for a smaller phone?

You've had the device for more than 1 month indicating the cooling off period is over - you've made a mistake in your question by the way as you've listed the same model smartphone twice - you can always put the device up for sale in the local newspaper or 1 of those online sales sites such as Craigslist - another option you have is to take the device to a pawn brokers though the shop is going to offer you a fraction of what's it worth - you'll likely get peanuts from the pawn brokers and they'll mark the product up way up in price

You might get away with saving everything to your icloud, selling the 6s plus and then buying a regular 6s then logging on and getting everything back. You could ask for a swap but i doubt apple would allow that. You may just have to make do and be glad that you have one.

You may just have to spend more time adjusting to your new phone. Most carriers aren't so lax about their exchange policies for phones. Honestly if I were you, I would just keep the phone and try to get used to it more because you'll save yourself the headache from dealing with your carrier or Apple.