Convert Classic Site Collection To Modern Site Within OOTB Feature

Microsoft has designed a Modern Team site experience to makes it easier for anyone to create beautiful, dynamic, and mobile friendly sites.

Microsoft has designed a Modern Team site experience to make it easier for anyone to create beautiful, dynamic, and mobile-friendly sites. This article explains, how to convert your classic site collection to a modern experience site. 

Today, a modern site can be created under Office 365 Group with template STS#3 or sub site of any classic site but there is no option to create a root site collection with modern experience. But what we can do is, convert our classic site collection to modern experience with merely a few clicks.
 
Let's create one new site collection with classic experience using Admin center.
 
 Convert Classic Site Collection To Modern Site Within OOTB Feature
 
Below, the site is created with the classic experience.
 
Convert Classic Site Collection To Modern Site Within OOTB Feature 
 
On all site collections,  there is an option, “Connect to new office365 group” except the root site collection because it’s not advised to change the root site collection as Office365 group.
 
Convert Classic Site Collection To Modern Site Within OOTB Feature  

This option will convert your team site to an office 365 group with the same URL. Click on "Let's get started" button.

Convert Classic Site Collection To Modern Site Within OOTB Feature  
Convert Classic Site Collection To Modern Site Within OOTB Feature  

Here you need to define a group. Provide group details and click finish.

You will see a brand new user interface.  
 
Convert Classic Site Collection To Modern Site Within OOTB Feature  

Conclusion

We just learned how to convert a classic site to a modern site.