To change the dino a player is using you will need to make some changes to the games database files. By following the steps below exactly everything should work perfectly.
1. Stop your server
2. View your files using either the File Manager or FTP (https://pingperfect.com/index.php/knowledgebase/19/Accessing-your-files.html)
3. Navigate to "TheIsle\Saved\Databases\Players"
4. Find your Steam64ID in the list of players - you can use https://steamid.io/lookup to find your ID
5. Look for the line "CharacterClass": "",
6. In between the speech marks add the type of dinosaur you would like to play, for example "CharacterClass": "HypoRex",
7. Set health, stamina etc as specified in the dino statistics - http://isle.wikia.com/wiki/Dinosaurs_List
8. Save your changes and start your server