An easy way to cut big models in half is to drop the portion of the model you don't want sliced below the print bed prior to slicing.
Drop the model to the bed.
Double click in the model. In the window that pops up on the right, near the top, deduct from the value currently shown in the Z direction, the amount you want to move the model into the bed. That amount of the model will drop below the bed when you confirm at the bottom of that window.
Slice the model. The part below the bed will be ignored.
Later, you can rotate the model 180 degrees about X or Y and repeat the process to print the other half.