Thank you Midnightdraven, I found the shared folder and did clean up all the files I didn't need as it was described on the thread I mentioned.
But may I ask you how does DM "knows" what OS I want to install on my BB? E.g. first I installed OS 220.127.116.11 on my DM, and then when I connected my BB to my PC it upgraded my BB from OS 4.2 to OS 18.104.22.168. Why 22.214.171.124 and not e.g 126.96.36.1997, or 188.8.131.52?