Contacts who have a Portal Access Level of Admin or Mid can set the Portal Access Levels for other contacts within their organization.
Once logged into the Portal the contact can access the Manage Users area.
In Portal Version 1 this is on the top menu:
In Portal Version 2 this is under Your Name:
All the Contacts for that Organization are listed here. To change the Portal Access Level for a Contact, click Edit next to their name:
Change the Portal User Access Level and click on Change to save your amendment:
The Portal Access Level can be set if your contacts want to invite new colleagues to the Portal as well.
Click on Invite User:
Fill in the new Contacts details and set the Portal Access Level before clicking Invite to add them: