It is completely natural for the plant to use the stored energy in those leaves for new growth. If your top leaves start yellowing or new growth is yellowing, it is an issue. Old growth on the bottom of the plant that is now not receiving as much light, and thus not making as much energy, will be used up by the plant. Dont touch them, once the plant uses all the nutrients it will seal off the leaf and the leaf will fall right off at the slightest wind.
