The default experience for most document libraries and lists has changed. This new, modern experience is recommended for most lists and libraries.
Note: The following steps change the default experience for everyone. To use the classic experience just for yourself, select Return to classic SharePoint in the bottom, left corner of the page. To exit, select Exit classic experience.
Change the experience for a list or document library
In the modern experience for a list or document library, select Settings , and then select List settings or Library settings.
In the classic experience, Library Settings or List Settings exists on the ribbon.
Towards the end of the list of settings, select Advanced settings and select List experience.
Select one of the three options, and to save, select OK.
Change the experience for all lists and libraries on a site
You can activate the site collection feature SharePoint Lists and Libraries experience to set the classic experience as the default for an entire site.
When both the site collection feature is active and the List experience for a list or library is set to New experience, the new experience is used.