To change the modpack on your Minecraft server, open the More menu in your server panel and go to the Modpacks page. Select the modpack you want to use and apply the change from there.
Before changing your modpack, it is recommended to create a backup in case you want to restore your current setup later. Once the new modpack is applied, your server files and required components will be updated based on the selected pack.
After the process is complete, restart your server and make sure your game client is using the same modpack version.
If you need help with this, please submit a ticket.