To enable Alpha 17 Experimental, you will need to do two things. The first is to set your server to the latest experimental build.
Go to the Control Panel for your 7 Days to Die server. On the Map drop-down, choose either "Navezgane (Experimental)" or "Procedural (Experimental)" Go to the bottom of the control panel and click the green button to restart the game server.
To play on your server, you must delete the data from your Alpha 16.4 saved game. You can do this by connecting to the server with FTP and opening up the Saves folder. Find the name of the folder that corresponds with the map you're using, then delete that folder. Go back to your Control Panel and restart your game server and you will be good to go. Once you complete those steps, now you need to set your Steam client to run 7 Days to Die experimental mode.
Go to your Steam Library Under the list of games, right click on 7 Days to Die and choose the Properties drop-down. On the pop-up window, the far right tab will say BETAS, click on the tab. On the drop-down menu labeled "Select the beta you would like to opt into:", choose the "latest_experimental - Unstable build" option. If you are unable to see this option, then restart your Steam program and try again. If it does not appear, even after that, then it's possible that the alpha build has been delayed. Once you do that, click on the Close button at the bottom of the window. 7 Days to Die should start downloading an update now. If it does not, restart Steam. Once 7 Days to Die is ready, start the game up and you should see an indicator on the main menu that says you are running Alpha 17.