First, chill a bit: human beings have coexisted with various molds for millions of years, and molds are relatively harmless unless you are immuo-compromised or spend 24 hours a day in a sealed room with the stuff. You are probably in greater danger of ulcers worrying about the molds than from the molds themselves. If you are still worried, wear an N95 mask that you can buy at home supply stores.
Anyway, you can do this yourself:
1. Get a dehumidifier.
2. Find the sources of any water entering room and fix them. No amount of cleaning will make any long term difference in you keep allowing water to seep/leak/drain in.
3. Open windows to room as much as possible.
4. Mist down the moldy area to limit dry spores getting loose.
5. Seal off area to be cleaned so you limit any spores you stir up.
6. Treat the mold with several disinfectants to increase likelihood that you will kill the species of mold you have (I recommend a chlorine bleach based treatment, a peroxide-based treatment, and a quaternary ammonium solution). Be sure to first completely remove disinfectants applied before going to the next disinfectant, as there can be chemical reactions by mixing disinfectants.
7. Throw away all materials used to clean up the mold in a sealed trash bag (i.e., do not take your dish scrubber and then take it back to the kitchen). If you collect the leftover water and cleaning solutions in a bucket, do not dump in an interior drain, or the mold will have a potential place to regrow.
7. Repeat as necessary.
After the room is cleaned and dried, consider redecorating the area with a mold-killing paint.