The system will combine them only if they have the same social security number – you will have to change them to match if you want it to work. Choose:

Setup / payroll / employee utilities

Under ID Maintenance at the very top is the Change or Combine ID utility. Click the List Button to select one of the employee and then click the ‘combine’ button just below. If it finds the second employee (by ssn) it will show it in the list that pops up. Just click OK on the right to combine.