Don't want to mess it, let's recap:
1. backup everything to external drive, must be fat32?
http://www.gamefront.com/how-to-backup-your-ps3-hard-drive-and-save-games/
does it backup all games, saves + all accounts i have on ps3?
2. change drive
http://www.gamefront.com/how-to-upgrade-or-replace-your-ps3-hard-drive/
3. restore back all
Y/N ?
1. backup everything to external drive, must be fat32?
http://www.gamefront.com/how-to-backup-your-ps3-hard-drive-and-save-games/
does it backup all games, saves + all accounts i have on ps3?
2. change drive
http://www.gamefront.com/how-to-upgrade-or-replace-your-ps3-hard-drive/
3. restore back all
Y/N ?

I just inserted the 500gb ps4 hdd in my 12gb ps3 and it formatted it and kept all my gamesaves on the 12gb bit. Only thing I did was uninstall game installs like gt3.