You need to be a workspace admin to change roles.
Create a role
Open Settings > Permissions.
Choose Add Role.
Give it a name. Choose a Role Color if you like (it appears on badges).
Under Permissions tick what the role may do. They are grouped by area (Wall, Sessions, Staff, Moderation and so on). Expand a group to see its permissions.
Under Group-synced roles tick the Roblox group ranks that belong to this role. Each rank can belong to only one role.
Choose Save Changes.
If you see Setup API Key, the workspace has no Roblox Open Cloud key yet, which Rosterr needs to read your group's ranks (see "How do I create a workspace for my Roblox group?"). Use Sync Group afterwards to pull the latest members.
The newer role editor
Workspaces with the newer editor also get:
permissions grouped by area, each with a plain-English description,
search across permissions,
a preview of unsaved changes and a check of the role before saving,
starter presets when you create a role (see "Common roles you can start from (role presets)").
Edit a role
Open it, change anything, choose Save Changes. People with the role get the new permissions within about half a minute.
Delete a role
Choose Delete Role and confirm. People who had only that role lose access. They are not removed from your Roblox group. You cannot delete the Owner role.
The Owner role
Its name, permissions and rank connections cannot be changed: they are managed automatically so someone can never lock the owner out.
Common mistakes
Forgetting to connect ranks. The role exists but nobody is in it. Connect ranks or add people manually.
Ticking Admin by accident. Admin grants everything. Untick it and use specific permissions.
Two roles needing the same rank. Not possible. Combine them, or use manual assignment.
Related articles
Roles and permissions: the basics