For each space, the person who created the space is automatically designated as the admin, although they can make other people in the space an admin if they'd like. The admin of each space can control a lot of different settings within the space, and it is all done by navigating to the settings by clicking the gear icon in the bottom-left corner and clicking on the appropriate space

The below window appears after clicking the gear icon. Here you can update the icon or name for the space, record a welcome message that will be the first video seen by anyone who joins the space, and manage those who are in the space as well as deciding who can invite others into the space. 

To make someone else an admin (there can be more than one admin), click "manage space members" then click the three dots next to the person's name that you want to make an admin, then click "Make admin". Removing someone from a space is done the same way but instead, clicking on  "Remove from space".

In this admin menu, you can also copy the link to invite space members, integrate the space with Slack, and disable forwarding, public links, or downloading for the space as a whole.