Any user can be made an Admin. The scope of their administrative ability is limited to where they are placed in the workspace's group hierarchy. Let’s say your workspace has the following Group Hierarchy
If a user is placed in West and made an admin, she will have the ability to manage users and circles within West, Los Angeles, and Seattle. She will not have visibility or administrative powers over circles or users located in other groups.
Follow the instructions for Editing a User’s Account to make a user an admin.