There are a few ways to change the employee's job title:
Assigning a completely new job to an employee?
You will need to first create and approve the new Job Description. After the saving the Job in the "Review & Approve" step, there is an extra step where you'll be able to assign employees to the Job.
Does the Job already exist in your Job list?
Click on Employees in the top navigation bar, and then click on the employee's name. You can select a new Job Description from the drop down list of jobs. Make sure you confirm the new choice or click 'Save' at the bottom of the page.
Only want to make a minor change to an existing Job?
If you just want to make a minor change to the existing Job Description then click on Jobs in the top navigation bar and then click on the Job you wish to change. When you are finished, make sure you hit Approve at the bottom of the page.