If you are a team administrator, you can change many aspects of jobs, such as their name, color, and who is qualified to do the job.
First, head to your team's template page by clicking on its link in your team's navigation area:
There, find the job name that you would like to edit from the list of jobs on the right-hand side and click the edit (pencil) button next to it.
Making changes to the job's name or color will also change the name and color of each existing shift of that job. Make sure to always click "Submit" in order to confirm the changes.
Making changes to the job qualifications will affect the current qualifications of your team members.