Yes, when you update, all your existing work disappears, but if you’ve made backups with C6, you can restore them back, no problem there…
To restore them where you want them, once you have updated the firmware, go to :
→ Global menu ([FUNCTION]+[GLOBAL] on the mini keyboard)
→ SysEx Dump
→ SysEx Receive
There you can select what and where you want to receive : kits & sounds can go into projects & soundpool, you can select into which +Drive banks to put the sounds, etc. Quite flexible. Don’t be afraid, the new OS is really much better organized and powerful !