Hi Sergio

> Is there any issue that I must be aware of?

The best thing for you to do, is to read the Firebird 2.1 release
notes, found at
http://www.firebirdsql.org/rlsnotes/Firebird-2.1-ReleaseNotes.pdf

The release notes contain a full explanation of all the changes that
have been made to Firebird - for any of us to list them out here would
just repeat everything in the release notes.

> I will make backups of all my databases with 1.5, then install 2.1 and
> restore all databases
> That's all?

As far as I can tell, the most important sections of that document
relating to upgrades are Repairing Your Metadata Text, which starts on
page 100, and Dealing with the New Security Database, which starts on
page 115. There may be other changes made since Firebird 1.5 that will
impact on the way you use Firebird, and you should review the whole
document for impact on your applications.

> I've been reading that there are some issues when you change the properties
> of some fields in 2.1

This could be the issue addressed in the Repairing Your Metadata Text
section I mentioned above.

> I also read that a general rule is: for win32 you must install Superserver archiqueture. Is that ok?

Take a look at this page from the brilliant Firebird Quickstart guide:
http://www.firebirdsql.org/manual/qsg2-classic-or-super.html

All the best
Gareth Marshall