Former banking equipment installer/technician checking in: From your description, do I correctly presume that the safe has no wheels? If that’s the case, it’s still a simple task.
Tool list- a tapered pry bar, one with a gradual slope, one or two regular crow bars, three or four lengths of 1/2" steel rod stock-they should be a little longer than the safe is deep-you can buy these at a Home Despot.
First, sweep the garage floor. Be thorough, as a tiny stone will become a great impediment. Assuming you’d like to use this safe in it’s final location, check the level of the floor there. It doesn’t take a lot of error to put an open or closed run in a heavy safe door. If the floor is off, you’ll need some metal shims- around 4" square-available from a local steel supplier of sheet goods or a metal fabricator.
To move the safe, take the tapered pry bar, place it about a third of the way back from the safe front (they tend to be face-heavy) and tap it in with a hammer to get some purchase. Continue to lift it in this fashion until you can get one or both of the regular crow bars under the two corners, about an inch or two from the outside faces. What you’re working towards is being able to lift one side of the safe about 3/4" so a solid rod can be slid underneath:
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Then go to the opposite side of the safe and tap the tapered bar underneath at the midpoint, and then lift. Longer bars make for less effort, naturally. The safe will scoot a little bit and the rod will be moving towards the middle of the safe. Repeat until it’s not quite halfway:
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Stick another solid rod under the edge where you started-it should easily fit without lifting as that end of the safe will be higher.
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The next time you scoot the safe, it should be fully raised off the floor by 1/2" and can be easily moved a little at a time using the crowbars between the floor and the safe underside.
You just have to watch where the bars are in relation to the balance point and keep it supported so you don’t have to start over. As you can see, the safe is on the first two rollers, and is ready to ride onto the third. By the time the first is no longer in bearing, it will need to be moved to the front again.
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Repeat as needed until you get it where you want it, then remove the rods by reversing the insertion procedure. Then check the safe for level and plumb, door runs and/or bind. Correct as needed with shims, and then get someone with proper tools and experience to set the combination. You don’t want a lockout after all of this. 