How to delete Sharepoint content types from Sharepoint admin center?

Step 1: Sign into Office 365 admin portal via https://portal.office.com

Step 2: Click on Admin from the left pane and navigate to All admin center > Sharepoint.

Step 3: Click on Content Services on the left pane and click Content type gallery.

Step 4: Select all the content types you want to delete in the page.

Step 5: Click on the Delete button on the top-left corner and click on Delete on the pop-up.