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 18.104.22.168 on my DM, and then when I connected my BB to my PC it upgraded my BB from OS 4.2 to OS 22.214.171.124. Why 126.96.36.199 and not e.g 188.8.131.527, or 184.108.40.206?