You can delegate subdomains to another DNS provider like Amazon by setting NS records for those subdomains and pointing them to Amazon. But I don't think that's what you're asking.
If you want for some reason to point the whole zone to Amazon so that Amazon provides DNS for the domain, then the place to do this is at the registry. Of course that means any records you've set up in tinydns, SOA, NS, A etc are irrelevant.
There are no standard NS entries for Amazon and you need to jump through their hoops before they tell you which ones to use. Then enter those name servers into Registro.br, and complete the configuration at Amazon or whichever DNS provider you choose.