Your current installation needs to be upgraded.
Please, pretty please, it is recommended that you backup your database
(you should do this regularly anyway)
Nothing awful should happen, but this doesn't mean it won't happen, right? ;)
On every step, if something goes wrong, you'll see a message and hopefully a way to fix.
If everything goes too fast and you cannot read, good for you, let it go :)
Once you are ready, press "Upgrade" !