what is the main difference features forum 3.0 to 3.1
We've published a list of all significant changes between WoltLab Suite 3.0 and 3.1, let me know if you have any other questions in this direction: Features and Improvements in WoltLab Suite 3.1.
Absolutely! You're prompted for the installation path at the early stages of the setup process, just change the installation directory of the Core and the Forum and you're done. If you want to migrate a live installation, then you'll need to follow this guide: Change directory structure.