Backup Exec 10d is ~13 year old product and has been EOS/EOL for a long time.
I think the product did not support 64bit media server operating systems back then.
Backup Exec 16 only support 64 bit Operating system for the Media server itself.
If your current BE 10d is 32 bit server then that may limit your in place upgrade scenario.
In order to get to BE 16 (Direct upgrade paths) you would need to upgrade to Backup Exec 11d first in trial then BE 2010 R3 trial.
The above assumes you can get a hold of 11d and 2010R3 media to upgrade. 11d, 12.5, 2010R3 are EOS products and the install media is not avialable to download from Veritas.
If you can find these older install media AND assuming your media server is 32bit OS you could use the Backup Exec migration Assistant to Migrate everything to a 64 bit server with Backup Exec 16 once you get upgraded to BE 2010 R3. https://www.veritas.com/support/en_US/article.100041264
With the above being said it may be best to start fresh with BE 16.
The media (Backup to disk or tapes) used in BE 2010 can be restored/cataloged in BE 16, etc.
Another thing to consider is what your backing up. If your backing up any remote machines are the compatible with BE 16. https://www.veritas.com/support/en_US/article.100032806
