If you are currently making the contributions on a pretax basis, you cannot change the insurance. You elect the insurance in 1 year increments and this is one of the rules. It's a IRS law called Section 125.
The only time you can change the election is via a life event (marriage, divorce, baby, etc)
If you are paying aftertax, you can change your benefits at anytime. All employees are ALWAYS allowed to elect benefits on an aftertax basis but you probably need to personally notify the company because the election will normally default to pretax payments.