怀念：reminisce; to think of; to cherish the memory of 想念：to miss; to remember with longing; to long to see again

When we use"怀念"along with some special periods or time eg，好怀念童年时光啊，but "想念"along with something or somebody eg,想念家乡，家人

Thanks so much both

怀念To miss is to Miss the pass but 想念, may be a person, or a place, may also be a thing.

怀念 is to miss a thing that is gone, implying that it no longer exists or stays forever out of your reach. 想念 doesn't have that kind of meaning. You can use it freely.