How to enable Lightning Experience in your Salesforce Classic Org.?
To start, please Log In into your Salesforce and click on the Setup.
Next, please navigate to the left side of your page and click on the "Lightning Experience".
Please scroll down, and click on the "Disabled" button.
You will now be prompter with warning pop up. Please click "Finish Enabling Lightning Experience".
When done, you can Switch to Lightning Experience by clicking on your name in the top right corner.