How to change the blade on my mitre saw?
If the model number is correct, or even close to it, this may be useful for you:

Firestorm FS100L miter saw manual

From that link, I found this set of images that are sure to be useful:



A bit more digging in the manual shows this text:

WARNING:DISCONNECT MACHINE FROM POWER
SOURCE!


Remove screw (A) Fig. 41 and rotate cover (B) to the rear (Fig. 42).
To remove the saw blade, insert the hex wrench (C) Fig. 43 into the
hex hole located on the rear end of the motor shaft to keep the
shaft from turning.
Use a wrench (D) Fig. 44 to loosen the arbor screw (E) by turning it
clockwise.
Remove the arbor screw (E) Fig. 44, the outside blade flange (B),
and the saw blade from the saw arbor.
Attach the new saw blade making certain that the teeth of the saw
blade are pointing down (Fig. 44). Place the outside blade flange
(F) on the arbor, and attach the arbor screw (E) by turning it
counter-clockwise using the wrench (D). At the same time, use the
hex wrench (C) Fig. 43 to keep the arbor from turning.
Rotate the cover back to the front and replace the screw that was
removed in STEP 1.


WARNING:Remove wrenches (C) Fig. 43 and (D) Fig. 44 before
starting machine.

Step 3 confirms reverse thread on the bolt holding the blade, turn clockwise (analog, not digital) to loosen.