You are in luck. It is adjustable-length (3 holes and it's in the middle one).
Hold your bike upright and measure the height from the ground to a convenient reference point (so that you will be able to see how much change it makes).
Find a way to support the rear of the bike off the ground without carrying the load on the suspension (a normal paddock stand will not work). In my shop I do it by hanging the back of the bike from tie-down straps. Sometimes you can do it with a block of wood under the side-stand and a jack of some sort under the other side.
Loosen the nut, push the bolt out, move the rear wheel so that the next hole lines up, insert bolt, tighten nut.
Then re-do your ride height measurement and subtract the original measurement from this one. That's the amount of difference you made.
As a first-guess, you should push the forks down through the triple clamps by this same difference so that you make (roughly) the same difference front and rear. Don't overshoot stock ride height (generally, the top of the fork should not be recessed below the top of the handlebar / triple clamp).
Raise the front of the bike using a steering stem stand (so that the weight is off the front suspension).
Undo the triple clamp bolts for one side, push the fork down in the triple clamps to your desired position, re-tighten the clamp bolts. It may be necessary to release the handlebar clamps and reposition them. Then do the same for the other side.
Total cost: $0.