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These come in UPFLOW and down flow models, If the air comes out the top and is drawn into the bottom or side at the bottom, the entire blower assembly slides on rails... there is a retainer screw at the front end of each rail that needs to be removed to enable that.
If you have air conditioning attached you will also have a cooling coil, with two copper tubes connected, if that coil is on top of the furnace you have an upflow furnace.
Let me know what you have, we can go from there without a time limit.