how to safely take out a coin from a protective holder?

The value of the coin(s) is greater while still in the slab (sometimes significantly) but if you really want to break it out try a vise. Place the slab in so that the seamed edges are the sides touching the metal of the vise. Go slowly until the slab cracks. From there try to remove the coin.

It is best not too but in some cases people break them out to send in again in the hopes of getting a higher grade. A hacksaw will cut off one end and then you can use a knife or object to pry the haves apart. One must be very careful and take ones time. I have found no two open exactly the same. I usually don't do it unless I feel the grading company really screwed up, which can happen.