To add or edit admins, click on the cog/gear in the bottom left-hand corner and then select "Settings".

Here, you want to make sure you have selected the admins tab:

Once this is completed, your page will look like this:

Admins can see everything and edit/change anything.

Users are similar to admins, apart from they are unable to add new users/admins.

Restricted Users can add information, but are limited in what they can access.

On this page, there will be a bar allowing you to Add/edit admins. Here you want to input the email of the person you would like to add, and select from the drop-down list whether you are adding them as admins, users or restricted users:

If you fill out the new admin's email address in the box at the top and then click "Invite", the admin will then get a link in their email. Make sure that they check their junk as it sometimes ends up there. You will see them listed in the "Pending Invites" list:

Once confirmed, they will join other admins under "Existing Accounts". You will then see all of your accounts listed there:

Here, you can change whether an account is an Admin, User, or Restricted User, by selecting the toggle above. You can also remove accounts altogether.