This the step to activate the 3.0 Public Beta

"Firstly to get the 3.0.0.1 update:

1. Open your steam library.
2. Right click on Unturned in your list of games on the left side of your screen.
3. Click "Properties."
4. Click on the "Betas" tab.
5. In the Key box type "OPERATIONMAPLELEAF" without quotes (case sensitive).
6. Click "check code."
7. In the drop down menu above the key box select "preview - Public test branch."
8. Click "Close."

To go back to 2.0 version, just change from "preview - Public test branch." back to "NONE", then wait for the 24MB update.