When your candle has completely burned down, you may choose to recycle the entire glass container with the wax in it. However, if you would like to reuse the holder, take any remaining wax out of the holder. This can be done by placing the holder in hot water or by placing your holder (if it's oven safe) in an oven set at the very lowest setting (usually "Warm"). Alternatively, you can use a hair dryer to soften the wax in the glass. Once the wax is soft, it may be scooped out or even wiped out with a paper towel.
You may dispose of the leftover candle wax by throwing it in the trash (your own trash if the spell was to bring something to you or a trashcan away from your home if you were doing uncrossing or banishing work), however, if you would like to dispose of your candle in a more ceremonious way, you have several options.
If you have been working with an invoking candle, you may keep it in a ziplock bag and place it in an appropriate place (such as your bedroom for a love spell or your office for a prosperity spell) until your spell comes to fruition. Alternatively, you may bury it on your property or in a potted plant in your home or workplace. You might want to form the leftover wax into symbols such as hearts or dollar signs and place these wax talismans on your altar or add a small piece of the wax to a mojo bag. You can also soften the wax with a hair dryer and use it to form a poppet or doll baby.
For an uncrossing or banishing candle, you may want to bury it somewhere away from your home, bury it in a graveyard or leave it in a crossroads, that is, leave the spell remains in the center of a quiet intersection where two roads cross.
In any case, once your candle has burned completely, your spell work is complete. Your work now is to envision, expect and receive the positive results.