In real life, destroying a whole building isn't as easy as it seems in the cinema. If a garage has become unusable or unwanted, it has to come down. You will have to plan carefully and apply for any local permits. Additionally, make the surrounding area as safe as possible so that there won't be any unwanted damage when the garage is being destroyed.
Check with your local municipality and apply for any necessary permits for demolishing your garage.
Rent a large metal trash container ahead of time and make sure that you have enough room on the property or the curb for it to sit in.
Turn off any utility lines (water, gas, electric) that connect to the garage. Shut down the breaker(s) connected to the garage and pull the switch(es) free of the box. Remove the garage's wires from the box, as well. Double-check that everything is off by turning faucets on and off, and testing for live voltage on switches and outlets.
Remove anything you can reuse, including fixtures, outlets, building trim, windows, plumbing and doors, and set it all aside where it won't be confused with rubbish. Remember to dismantle garage door openers and other installed mechanisms.
Prop a ladder against an outside wall, with an assistant to steady it, and go up to the peak of the roof. Pry off the roofing material, using a pry bar and hammer, working downward until only the shell remains.
Use a circular saw and, starting from the peak of the roof, cut out the shell and the framing by pieces, which you can let fall to floor.
Standing on the ladder, hook the claw of the hammer over the top edge of a wall board and work it free. Remove nails as you go and let any siding to fall into the pile. Saw out any wall framing.
Sort out the usable and recyclable material from the rubbish. Store what you want and make pickup arrangements for the recyclables and the trash container.