Steel toe boots are work boots that have a steel toe section to protect the feet from being crushed or stomped on. While it is possible to remove the steel toe from the boot with some work, you'll need to replace the toe with something to make the boots wearable again. Additionally this is a task that may damage the boots beyond use, so if the boots from which you're removing the toe are irreplaceable, then you may want to reconsider.
Cut the seams holding the toe to the rest of the boot with your utility knife. You'll need to cut the half circle along the portion that holds the toe to the section where the lacing begins, and you may need to cut the section along the sole of the boot as well if the toe is anchored there as well.
Open the hole between the toe and the rest of the boot by pulling back the leather. Make sure there aren't any strips of material or thread holding the steel toe cap in place with the rest of the boot.
Grip the steel toe with your pliers and twist it back and forth until the steel toe cap comes free. You should be rocking the cap back and forth as well as side to side. Keep pulling until the cap comes free.