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 184.108.40.206 on my DM, and then when I connected my BB to my PC it upgraded my BB from OS 4.2 to OS 220.127.116.11. Why 18.104.22.168 and not e.g 22.214.171.1247, or 126.96.36.199?