If you go to the kde4 support section of the forum, you will find detailed instructions on how to do the update.
But, the release is so close that we can all taste it. We are all like children who have found that our parents have put a lock on one of the closet doors a week before Christmas. We know that there is something really exciting coming very soon.
If I were you, I would just find the best way to back up any data on your current install so as to be ready to install the new version when it is released.
Normally on a rolling update system like this, you could just update your existing system.
But this time, Tex knows that we are like a bunch of children who do not want to wait while he creates all the changes and mechanisms needed to insure a safe update for most everybody.
So, he has already told us that he will release the new version so as to be a new install rather than an update.
Personally, I am glad. For those of us who do not yet intimately know the inner workings of Linux, it is nice to know that we are not starting out with some unknown time bomb in our system that we inadvertently created some time in the past.
Also, every new system has different artwork which so far has never shown up when doing an update.
For those of us with multiple systems and bad memories, having new artwork helps us to shift gears in our thinking when we boot into the new system.
I usually create new partitions on my drive and install the new system to them until I am used to it. This way, I can still access all the files in my original install from the new one. And then, when I am comfortable with it, I delete the old one.
Another advantage to doing it this way is that all the various configuration files are still accessible so even though I have forgotten how to do some of the network setup. Or maybe the user interface has changed, I can go compare the old and new files and figure out what is going on if something does not work as it did before.