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If you lower the level in the tank the bowl won't have as long to fill and that will lower the level in the bowl somewhat. But if you lower the level in the tank too much the toilet won't flush properly.
It's trial and error. There is an optimal level indicated by a mark on the tank or overflow pipe. Beyond that you just try different levels and see if you still get a good flush. You adjust the level by setting the float height on the fill valve (on the left with the adjustable rod).
Should be counterclockwise on most models. You're going to need to do some experimenting so you'll probably wind up working the float in both directions
So how did it work out? if you still get a good flush at the lower tank level but the bowl level is still to high then you can keep lowering the tank level until it doesn't flush right