Well, you simply need to buy a license and use it ingame. If you plan just to drift maybe a S2 license feeds your need.
This will open the way to the other servers.
If you mean how do you update to the latest patch (LFS0.6R), in LFS go to Multiplayer > Display list of hosts > Choose a download mirror
If you mean how do you access more content/licensed servers, head to https://lfs.net/shop and purchase a license. I recommend an S2/S3 license as there aren't that many active S1 servers these days.