I just discovered what I assume is mold on my window frame in the kitchen/living room (quite high humidty, but the window has been open a lot and our fan is going 24/7). Now, I've been told that dealing with black mold is dangerous, my landlord however looked at it and said it can easily be dealt with with bleach. After googling this I'm still not sure if I can or can't deal with this myself, some say I should get him to get someone to do it professionally, others recommend everything from bleach to special paint. What is the right way for me to deal with this?
That looks pretty bad. Don't use bleach, use a purpose-made mold killer product. I like Mold Armor, myself. Be careful with these products. They're super caustic and you could probably hurt yourself if you drink them or don't have good ventilation.
I think that the landlord is responsible, but sometimes it's necessary to do things yourself... that depends on your living/renting situation.
Household (5%) bleach (dilute 1/2 cup bleach : gallon water) will absolutely work. The black mold is probably Aspergillus niger, which often produces something called aflatoxins, which can cause cancer. But the danger involved with cleaning it off of a few windows is overrated compared with chronic exposure from living with it, eating it, or cleaning it up on a daily basis (ie., people who clean or remove mold for a living). But if you are concerned, use a dust mask.
Mildew resistant paint would be a good idea, after you clean it. But more importantly, the reason for the mildew is moisture; maybe it's from humidity/condensation, but usually the problem is that the window is getting rained on, and water is collecting on the sill. Preventing mold should start with weather protection. If high humidity, is the issue then a dehumidifier should be used.
I had mold in the basement bathroom. We installed a window which can be opened, a small humidifier, and cleaned mold with bleach. Advice for bleach, I emptied window cleaning spray container and sprayed bleach rather than using a cloth or something else. Works like magic. No more mold.