Exists a few guidelines to follow. All specified in the Migration Guide.
But, Considering you are migrating in the same version (9.40 32bits -> 9.40 64bits) , theoretically don't have any problem and take less then 4 minutes, the basic steps are:
- install the new version (64 bits) in other directory
- copy your enviroment ( set of variables like INFORMIX*) pointing to new dir
- copy your configurations (onconfig,sqlhosts) to this new directory
- execute a backup Level 0 ( Murphy Laws still exists )
- put your instance in quiscent
- force a checkpoint and jump to next logical log (onmode -c ; onmode -l )
- wait for all logical log backup (and save this backups! )
- shutdown your instance
- open new session pointing to new installation (64 bits)
- start your database
- drop all update statistics distributions
- execute update statistics
- And your IDS is free to your users...
I already do this in a IDS 7.31UC2 to 731.FC2 in HP-UX 11.0b with an 700GB database ...
In some cases have more steps like , remove all ALTER-IN PLACE and other little steps. All this are in the Migration Guide.
My suggestion , read the Migration Guide. Is a very small manual.
Just to remember , if you have clients program executing in the same machine and accessing the database with onipcshm (shared memory) , your client application will must be recompiled with 64 bits IDS client , or , you change the type of connection to onipcshm or onsoctcp .