Add the new Health Insurance Company through Manage Vendors.
Add a new Earn/Deduct Code for the new company. The Description will be the defining feature between the new and old.
Add the Vendor to the new Deduct Code.
In the Employees Misc. Deductions tab, use the [Add] button to add this new deduction. Take the check mark off the old one. Enter the new amount to be deducted each month or each paycheck.
PLEASE NOTE: The next time you process payroll, make sure you reset this employee to make the changes reflect properly in the payroll.