Try to preserve as much of the glue by working really slow here. If you pull too fast, the glue will separate and clump together, which will cause connection issues later (too much space between the battery connector and the battery).

I didn't have much success using a prying tool and caused a lot of damage at the place that is suggested as the starting point. I then saw the comments about simply applying pressure to the shell and this worked wonders. Just heat up the earburd and then put it in a clamp or a small vise. Apply some gentle pressure like cracking a nut and it will open up along the seam. This enables you to slide in a prying tool without damaging the outer surface.