Can't increase my disk size
When I've had to resize BootCamp volumes in the past I would use CampTune from Paragon.

It looks like they added support for Catalina recently, so it should work well for you.

As for removing the BootCamp partition altogether, I've always used the Boot Camp Assistant to do that. 

Note: It's recommended that you make sure you've backed up your stuff before adjusting partition settings with either the CampTune, Disk Utility, or Boot Camp Assistant. I've had situations where things go south quickly when adjusting partitions.