You can add and manage the Roles for the Portal Users from the Portal User Management -> Roles. You can Filter the records as per the Relationship Type, Is Default, and Status. 
Relationship Type: You can filter the listing of the Roles by selecting the Relationship Type either “Contact” or “Account”.
Is Default: You can filter the listing of the Roles by selecting the Default selected Roles (Yes) or Non selected roles (No).
Status: You can filter the Roles by selecting the Status of the Role either “Active” or “Inactive”.
After selecting the Filter options, you need to click on the Apply button to filter the Roles records. 
Here the listing of the Roles is filtered as per the Relationship Type ‘Account’. If there are multiple records of the roles, you can easily search the specific records by filtering the options.
By clicking on +Create, you can add a role for the portal users. Insert the Role details and the Relationship Type to select the relationship associated with the Role. 
Enable the Modules you want to enable for the portal users.
The Relationship selection is provided to select the relationship that is created in Module Builder between the contact/account and the Module. 
- From the list of the Portal user roles, you can change a role to the users (contacts) that were already assigned and can replace it with another role as you want to assign.
- By clicking on the Replace Role option, a pop up will appear to select another role from the drop down list.
- Once you select another role, it will replace the current one and assign the new role to all the contacts (portal users).
Note: Here in the drop down list, only those Roles will appear whose Relation Type is common.