Guide

1. If you are in the Salesforce Classic view, you will be able to see Switch to Lightning Experience over here.

2. It will take a few seconds to load. Your Salesforce theme and UI will then change to the Lightning Experience

3. If you want to switch back to the classic view, head over to the profile icon on the top right.

4. The dropdown shows Switch to Salesforce Classic. Click on it to switch back.

5. And there you have it! You can now switch back and forth from the Lightning View to the Classic View.