Mancesa is a brand owned by Corona, a Columbia-based manufacturer of china products. They own Mansfield in the US.
Some older Mancesa toilets don't have a siphon jet (the 1"-ish hole through which water flows to push stuff out of the toilet), and instead just run water into the bowl around the rim. If yours does have a siphon jet, make sure it isn't clogged (rubber gloves on, finger in hole to make sure not clogged). I dramatically-improved the flush on an old American Standard that way. If no siphon jet, you're stuck with the flush. Is the water level in the tank where it should be (i.e. are you getting enough water and water pressure to do a good flush?). See if the water level is adjusted to where it is marked on the tank (or 1/4" below the top of the overflow riser on the flush valve). That's all I can think of without seeing the thing.
You also might give it a good plunge to see if there's anything stuck in there affecting the flush. The problem also might not be in the toilet itself, but that's not anything you yourself are likely to be able to do anything about.
Maybe you tell the landlord that the toilet isn't working properly in the master bathroom (see -- not toilet itself sucks but toilet "not working properly") and he needs to send a plumber around to get it working right, and you need a working toilet for what you're paying in rent. That would be my first approach after trying the limited self-help above.
Hope this helps.