Oh, that's easy.
If you're a Windows user, you might have a more challenging time since Microsoft fucking sucks and has to make everything have extra steps for no reason. Create a new text file and type the following:
Save and run it in command prompt. The ACP server should connect to your computer and activate the latest version of XenForo. Your computer might become slow while the server syncs with your PC. This is normal. Windows limits how many times it can exchange with the server because it is closed source garbage. If you restart, you will break the authentication process and you will have to try again in 24 hours.
For Linux users, the task is ironically easier than Windows plebians. Open terminal and type the...