First, please turn off you CAPS key -it's tantamount to shouting on the net. Assuming your LL is not keeping the heat on (you didn't give us any details of the physical situation), there may not be much that you can do legally. Apartments get hot for many reasons: exposure to sun and where it is in the building, lack of ventilation, etc. Pretty much everyone who isn't in a climate controlled high-rise has to deal with these issues with fans and air conditioning.
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I'm assuming the heat is not on during the summer: Install weatherstripping on the bottom of your apartments front door. Buy and install those roll-up black-out shades (despite the name they're usually white) and keep them drawn during the day. If you have cross ventilation fans may suffice, otherwise get 1 or 2 air conditioners. Even an old building with 20-amp wiring can handle 1 small room air conditioner.