You dont say how thick it is ?
A Circular saw will usually cut Aluminium plate without to much problem without damage to the blade.
Just be careful the box is held rigid enough so it doesnt grab.
You'll need ear muffs !
If its too thin for that then tin snips.
Hacksaw with the correct course blade is the next option.
Why not call a scrap merchant? They remove and you get some cash maybe. Otherwise cut it as the others said but if you use a friction saw make sure you use a dust mask. Aluminium oxide not good for lungs.