First go to the Account Admin page by clicking "My Job Portal"m(In the top right of the main page)
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User Settings > Users
Click on the user you want to add/remove roles for.
then drop the "Manage roles" panel down:
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Remove roles by clicking the minus button to the right, and assign roles with the "Assign Role" button (it will prompt a search)
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Note:
You can view available roles, what permissions they have, and who is assigned to them via Account Admin as well. You can find the page in:
User Settings > Roles
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Hope this helps