Every frame my code counts how many objects there in the type.
Could you clarify that a little? There are no objects "in the type" in BlitzMax as there were with Blitz3D and BlitzPlus because BlitzMax does not keep an internal list of them.
How do I delete an object from a type?
Again, it's not "from a type" because the type doesn't have a list of them, unless you've added one of your own. In which case you get rid of it by losing all your references to it. Remove it from any collections ( lists, maps, etc ) that it's in and allow any other variables holding the object handle to go out of scope and it just gets picked up automatically.
Essentially, objects are destroyed automatically as soon as you become unable to reference them.