Hey there, Pawel_10
What exactly do you see in Disk Utility about the drive, would you please post a screenshot? Here's how to do it: http://www.tomshardware.co.uk/faq/id-2176231/guide-posting-screenshot-forum.html.
If the rest of the storage capacity is not partitioned and formatted, I'd recommend that you check this tutorial and more specifically the "Enlarge Volume" part:
https://support.apple.com/kb/PH22240?locale=en_US
You could also test the SSD for errors by using its manufacturer's diagnostic tool.
Hope that helps.
Boogieman_WD