To change your Minecraft server version, open the More menu in your server panel and go to the Versions page. From there, you can select the Minecraft version you want and apply the change directly from the panel.
This is the recommended way to update or switch versions on GameTeam, since the panel handles the process automatically. You do not need to manually replace server jar files for standard version changes.
After changing the version, restart your server and make sure you are joining with the same Minecraft version on your client.
If you need help with this, please submit a ticket.