Thanks for asking - great question.....
The easiest way is to click on https://autode.sk/InventorBeta
Firstly you need to have a Beta account. If you don't already have one then you can create one from:
https://feedback.autodesk.com
Use your existing A360 login credentials or create a new account.
Or, once you have logged on to the Autodesk Beta site, under the Open Opportunities section you will see a link called Inventor Futures. Click on that to apply for access, (you will need to complete a quick survey to help us understand your Inventor usage/history/background before you are granted access.
More general info about Autodesk Beta's is available from:
https://feedback.autodesk.com/overview/
https://feedback.autodesk.com/faq/
Thanks
Chris (II)

Chris Mitchell
PDMS Customer Engagment Team
Autodesk, Inc.