Yes you can do it. You need to make sure that you do the following:
1. Get the full install of 4.1.4 (not sure if 4.1.5 is public yet)
2. Backup the Database.
3. verify you have the backup of the database (Very imporant
4. verify you have a copy of BES 4.0.2 in case you need to roll back.
7. Upgrade the database (this is part of the install)
8. If the upgrade of the database is done then you should be good to go.
If any part failes then I would do a clean uninstall of BES
Then restore the database backup that you took.
INstall BES 4.0.2.
(Maybe try again if you are feeling lucky. If it fails again post it here with the reason for the failure or you might want to call into RIM support.)