I'm replacing my thermostat - where is the electrical power shut off switch to the furnace?

I'm replacing my thermostat (heat only) and the instructions say to turn off the electrical power to the furnace (which I guess shuts off the voltage to the thermostat wires) before removing the wires from the old thermostat and attaching them to the new one. Trouble is, I've looked around my gas furnace... show more I'm replacing my thermostat (heat only) and the instructions say to turn off the electrical power to the furnace (which I guess shuts off the voltage to the thermostat wires) before removing the wires from the old thermostat and attaching them to the new one.

Trouble is, I've looked around my gas furnace in the basement and I can't figure out where the switch would be. I have a fuse box, I wonder if I should just remove the fuse, and if that would be sufficient?

Sorry, I'm a girl, and this is a bit over my head. But I don't want to spend more money to hire an HVAC guy about this.

THANKS!
Update: I should add that nothing is labeled, including any of the fuses in the fuse box....I would have to unscrew all of them. My landlord is a retard. I asked him to fix the thermostat two months ago, and I'm tired of waiting, so I'm trying to do this myself.
Update 2: Several people have mentioned looking at my breaker box. I don't have a circuit breaker box...it's a fuse box.
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