Step 1:The first thing that youll need to do, is enroll with GooglesAndroid Betaprogram.
Step 3:Once enrolled, you will need to accept the terms and conditions.
Step 4:Once that is done, Google will push the update to your equipment.
Be warned though, that this is a beta version which means it might have bugs and other issues.
We recommend backing up all your data before installing Android 8.0.
source: www.techworm.net