If you have no presets in Bryce 6 then there are two possibilities - the first is that you haven't downloaded all the files that you should have and then installed them all. there should be nine all together (I think) . they will install everything into the correct place.
the second is that you had one of the installers that was faulty (preset 1 I think) which has given you an extra layer of files that Bryce cannot use.
All your presets should be in their own folders within Bryce 6 
The folders should show as 
Bryce 6/presets/brushes
Bryce 6/presets/leaves
Bryce 6/presets/materials
Bryce 6/presets/objects
Bryce 6/presets/skies
Bryce 6/presets/textures
Bryce 6/presets/trees
Bryce 6/presets/treeshapes
Inside each of these folders there should at least be a folder called installed and possibly a folder called user. (There may well be additional folders if you have bought any additional objects or materials etc)
If they aren't there then you have not installed everything.
If any of these folders have an folder in them with the same name ie if you have
Bryce 6/presets/objects/objects then that is one folder too many. Take anything in the bottom folder out and place it into Bryce 6/presets/objects.
Any of the folders that you have in the presets in Bryce 5 or 5.5 can be copied into these folders but rename them first as you do not want to overwrite the installed or user folder.