When you purchase a server from us, we provide the latest available version of Paper (a high-performance and optimised fork of Spigot, which is a fork of Bukkit). If you'd like to play on your server using a different version of Minecraft, you can easily do so by changing the server version.
Select the server that you want to change the Minecraft version for on the panel.
Download the version of Paper you would like to use from https://papermc.io/downloads.
Open the file manager and delete the existing server.jar file by right clicking it and selecting delete.
Upload the desired Paper server version file that you downloaded previously and rename it to server.jar.
If you are downgrading the Minecraft version of your server, download a backup of your worlds, then delete them.
Start your server and connect using the desired version of Minecraft.