quick question about deleting an object from memory

[LavaCreeperKing]

Hi. So when you create an instance(I may be spelling this wrong) of a class you can add it to a list. You can also remove it from the list if you need to ,but my question is. When you do 

list.remove(object)

does that also delete the instance from the memory or is the instance of the class still callable? If so How can you delete the instance from the memory if you no longer need it? For example: you create a game, enter level 1, the level gets created and enemies spawn in, you finish the level so now you no longer need any of the objects that were created for level 1.