How do I change partition size of Boot Camp?

So I've just gotten into Boot Camp and Windows. I downloaded Windows 10 and set it up to have 40gb of the 250 gb I have on my laptop. I downloaded a few apps on my Windows system and rebooted my system back into MacOS to check the amount of storage left on my Bootcamp partition. I only have 4 gb left of the 40 gb. I've tried to use disk utility to change the size of my boot camp but it doesn't allow me. It only allows me to decrease the size of the storage for it, not increase it.