I use 2 pliers. One to grab below the
juice holes, and the other to grab just the top cap. squeeze tightly and
twist. work it back and forth a couple times and it will pull right off. It gets easier to remove after it's been pulled off the first time.
To reinstall, I line the top cap up where I want it, hold the head between my fingers (with the post sitting on the table) and gently tap the cap back on with a small hammer (or even the pliers).