?ukasz,
You should be able to update now:
sudo apt-get update
sudo apt-get install wolfram-engine
After updating the Wolfram Language $Version variable should be this:
pi@test-pi ~ $ wolfram
Wolfram Language (Raspberry Pi Pilot Release)
Copyright 1988-2015 Wolfram Research
Information & help: wolfram.com/raspi
In[1]:= $Version
Out[1]= 10.0 for Linux ARM (32-bit) (February 3, 2015)