When editing a position, the process is very similar to creating a position. First navigate to the positions module, which is found as a part of the recruitment drop down menu in the navigation bar.
Here you can click on the position that you would like to edit and it will take you to the update position screen. This screen will look similar to the create position screen, so if you need a refresher on the fields and what they are for, please refer to Create a Position.
Now you can perform any edits that you would like to make. Once you are done, navigate to the bottom of the page and click the 'update position' button. This will take you back to the positions module where you can see all posted positions again.