How to Become an Admin in Space Engineers

To become an admin, you will need your SteamID64.
You can obtain it here: https://steamid.io

Basic Mode

In Basic Mode, you enter your SteamID64 under Admin Settings.
Then click on Save and restart the server.

Advanced Mode

In Advanced Mode, the SteamID64 is entered in the SpaceEngineers-Dedicated.cfg file.
Find the following line: <Administrators>.
Insert your SteamID64 between these tags: <unsignedLong>Steam64ID</unsignedLong>
Replace Steam64ID with your SteamID.
It should look like this:

      <Administrators>
      <unsignedLong>76561197979226165</unsignedLong>
      </Administrators>

You can also add more than one admin:

      <Administrators>
      <unsignedLong>Steam64ID_1</unsignedLong>
      <unsignedLong>Steam64ID_2</unsignedLong>
      <unsignedLong>Steam64ID_3</unsignedLong>
      <unsignedLong>Steam64ID_4</unsignedLong>
      <unsignedLong>Steam64ID_5</unsignedLong>
      </Administrators>

Click on Save and restart the server.