Step 1 :
Navigate to the Users Listing Page from the side menu > Use the Search tab to find the specific user > Click on the user's name to be redirected to their User Info Page.
Step 2 :
Go to the Permissions page by clicking on the Permission tab in the top horizontal menu > Click the + icon to add roles > Select the roles you want to assign by checking the corresponding boxes > Click on Update Role to save the changes.