Move the existing backup system which is BE 12.5 to NBU7.5

Dear All 

I am new to this forum and would like your guidance and support. I have been assigned a tast in my office to move the existing backup system which is backup exec 12.5 to NBU7.5. We are using HP VLS9000 storage with a MSL 6000 tape library. I don't know where where should I start. Kindly assist me step wise, please.

**** Moved to new discussion from https://www-secure.symantec.com/connect/forums/netbackup-75-documentation ****