Hello @GABRIEL COSTA AMARAL ,
As you know, shrinking/decreasing an existing disk isn’t supported in the Azure, and can potentially result in the data loss. It's only possible to increase the size of a disk but not decrease it.
The same can be confirmed there: "How to expand the OS drive of a virtual machine"
A workaround would be for you:
1) Create a smaller disk. Attach it to a VM.
2) Move all the data to a new smaller disk, test it.
3) Detach and delete the bigger disk.
(If the reply was helpful please don't forget to upvote and/or accept as answer, thank you)
Regards,
Olga