Go to User from the navigation panel on the left side of the screen. Locate the user you want to assign a role to and click on the icon that looks like a pencil in a box.
A window box containing the previously saved details will come up. *The previously saved role is Customer Service*
Scroll down to the Select Role box and choose a new role for the user from the drop-down menu. *The newly assigned role is Sales Personnel*
Click on Update User to save your edit.
A confirmation tick pops up like in the image below indicating you have successfully edited the User's profile.