OP can use a cartridge to update to 4.X or 6.X to use MSET. From there, it's easy to install 9.2 via homebrew.You will want to get to 4.x so you can use rxTools to update to 9.2.
If you use a game to update PAST 4.x you will end up with no browser and have to also buy ANOTHER game to update to 9.0-9.2 and then also buy Cubic Ninja to use Ninjhax 2.5 which doesn't need a browser. You can search the web for games that include a 4.x update or another user might comment one (the only one I know off the top of my head is Virtue's Last Reward for euro systems, which by the way is an excellent game to own if you're only going to own one game. I think also Luigi's Mansion 2 USA is one but not 100% certain).
Oh yes I forgot about 6.x. So there's quite a lot of games to choose from, and finding a cheap one shouldn't be too hard. I note that the OP is in Brazil where video game stuff is notoriously expensive :-/OP can use a cartridge to update to 4.X or 6.X to use MSET. From there, it's easy to install 9.2 via homebrew.
I'm not sure how you plan on exploiting your 3DS now that you're on 8.1 without a browser. Since you didn't listen to the above advice about getting to 4.x or 6.x for MSET, your only option now is to find another cartridge to update to 9.0-9.2. From there, you'll either have to use Ninjhax or oot3dhax as your entrypoint instead of MSET.I updated with Smash Bros, now is in 8.1.0-0U
That should work.
Thank you Guys!