You could stop the Minecraft instance, use the main panel’s file manager to browse to the instance and delete it’s ModpacksCache.json file, and start it again.
If that still doesn’t bring up the latest version of the pack, you’d want to do the following:
- Go to FTB’s site and grab the modpack’s server installer
- Run the installer on your PC
- Upload the files to AMP over AMP’s built-in SFTP, not the one on port 22 (use WinSCP or FileZilla, connection details are in the upper right of the file manager)
- From there you set the NeoForge version to what the pack needs and you should be good