The 715Zi has 10GS/s FEs by default, while all other models have 20 GS/s FEs, so the first thing would be to check whether your 715Zi has the 4x20GS/s option or not (in the acquisition menus, you'll see what sample rates are effectively available).
In any case, I'm not too sure Lecroy really ever offered BW upgrade options for the 7Zi (it's mentioned in the data sheet, but I've never seen any BW-upgraded 7zi..., nor are any option codes mentioned for those upgrades, although there are some option IDs in the database for that...), and for the 715, this would have required the replacement of the FEs... as said, check in the acq menu what you have... If you don't have 4 x 20GS/s, you got a 'disguised' 715... :-(
The model-ID, serial, options & Co are stored on an EEPROM on the interface card, and none of the system menus allow to perform modifications at that level (although some have managed to read & write from the chip, but it was a whole bunch more complicated than it sounds...)
One thing that can eventually confuse the software (but not about BW...this is rather 'cosmetic') is when the computer name (in Windows) doesn't match the scope's serial.
Would be nice to have a few pics of the scope's 'About' and 'Options' screens...