No need to throw out the candle wax with the glass jar ... especially when you can save and reuse both.
This is such an easy process and requires no special tools or equipment.
Step 1: Poke Holes in Wax
Using an old pen, stab the wax five or six times. Make sure you hit the bottom glass each time.
Step 2: Fill Jar With Boiling Water
Using a tea kettle or pot, heat up some water until it boils.
Pour the boiling water into the glass jar.
The hot water will liquefy the wax, and the wax will float to the surface on its own.
Step 3: Allow Water and Wax to Cool
Let the wax and hot water cool, to at least room temperature.
While waiting, take the opportunity to remove any labels from the jar. The hot water will loosen the adhesive.
Step 4: Remove the Cooled Wax
Using the same pen as in Step 1 and your finger, remove the top layer of wax.
Place wax in a plastic bowl or bag for future craft projects.
Step 5: Take Care of Any Wax Remnants
Pour the waxy water in the toilet or a trash can. Do not pour down the sink, as the wax could clog the drain.
It's likely some stubborn wax may still cling to the jar.
If it's a small amount, use an old receipt or paper towel to wipe the inside of the jar.
If a lot of wax still remains, repeat Steps 2-4.