Owners and admins can change another teammate's workspace role.
Go to Settings > Members.
Find the teammate in the list.
Use the role dropdown next to their name and pick Admin or Member.
The change takes effect immediately.
If you need admin access yourself
You cannot change your own role, and there is no in-app way to request an upgrade. Ask an owner or an existing admin of the workspace to change it for you. You can see who they are on the Members page, where each person's role is listed next to their name.
What you cannot change here
The role dropdown only switches between Admin and Member. The workspace Owner is fixed: their role cannot be changed from this dropdown. If the Owner needs to step down or hand the workspace to someone else, contact Aracor support.