Not possible, it is impossible to help with a upgrade through a forum like this. A successful upgrade require hours of careful planning, and upgrade attempts in a closed environment.
If you need consultant help, contact your local Veritas office, they may be able to assist you find a consultant that can help you.
I suspect that you will find the operating system is not supported, so you are not looking at a straight forward upgrade, but more of a "re-platforming" exersise. Given that you are starting from a "unsuported" release it would be strongly recommended that you will need to get consulting assistance from a partner or Veritas PS.
Should you be looking to do this "in-house" there are many factors that you will need to consider, some of which are covered in the vast amounts of documentation, however you will need to look at multiple versios of documentaiton and look to perfrom multiple upgrades as you go between versions.
The quickest and lowest risk approach would be to re-platform using a Catalog Migration approach, This allow you to JUMP directly from 7.5 to the latest version of NetBackup. You should reach out to Veritas for a consulting lead solution, or you could contact Stone Ram who have a software based solution.