Some Physical Layers used with OBDII
CAN-FD is a different hardware layer. It is not compatible with "classic CAN" even though they are specified inside the same standard. So CAN-FD is not an "update" to CAN, it is an entirely new hardware standard.

It isn't meaningful to upgrade existing CAN networks to CAN-FD. You would need to change everything from scratch, both hardware and software. It only makes sense to use CAN-FD for new projects.

J1850 is something else entirely, it's yet another standard. I have never used it so I don't know much about it, except that it was fashionable around 20 years ago and Motorola released some special MCUs with hardware support for it back then.


  I don't need exactly to know how the protocol works


Well, you do need to know this in order to understand why CAN-FD doesn't make sense as "drop-in replacement". It's not just faster baudrate, it is the data part of the frame getting clocked faster to allow higher payload than 8 bytes, up to 64 bytes. But all the higher layer protocols are designed and specified to use up to 8 byte payload, so they won't be able to do anything meaningful even if given more bandwidth.