Exchange Applewatch

I bought an Apple Watch series 3 on the 2th and I’ve changed my mind about the model and want to exchange for series 4! I was in the store and they told me i could not use series 4 in Brazil, but talking to my friend, he told me I can use series 4 in Brazil! So they gave me a wrong information! It wasn’t my fault! Can I pay the difference and get series 4 as I just bought it?