I have a D16, I'm now on version 3.01. I'm assuming that you have a CD writer to do the upload, if you have then you can back the songs up first.
If my memory serves me correctley you don't loose any data but it's always a good idea to back up just in case; or maybe you are not up to the version where you can back up data yet if which case you've no option but to go ahead and do it.