Hi Deepika,
You'll want to make a stop at 8.2 before jumping up to 8.4.
7.5 --> 8.2 --> 8.4
This will allow the database and other configurations to be appropriately migrated.
The one thing I stress with any upgrade is to take backups - full backups of the database, and primary/ump \nimsoft\ directories.
With those things, you can roll back as needed if you run into issues during the upgrade.
Phil